diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..7ccdb6d26 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,7 +1,9 @@
 // Predict and explain first...
-
+// I predict the code will print "My house number is defines means undefined.
 // This code should log out the houseNumber from the address object
 // but it isn't working...
+// Explanation: address is an object, and address[0] looks for a property named "0", which does not exist.
+
 // Fix anything that isn't working
 
 const address = {
@@ -12,4 +14,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address["houseNumber"]}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..aa0aead82 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,7 +1,9 @@
 // Predict and explain first...
+// The program will show an error because an object is not iterable.
 
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
+// We cannot use a for loop directly to an object because objects are not iterable in JavaScript.
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..585875e9d 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,7 +1,10 @@
 // Predict and explain first...
+// The program will display the title and serving information, but it will not display the
+// ingredients correctly because we are trying to print the whole object.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
+//  ingredients:${recipe} converts the whole object into a string rather than showing individual ingredients.
 // How can you fix it?
 
 const recipe = {
@@ -12,4 +15,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..13fcc66a9 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,8 @@
-function contains() {}
+function contains(object, property) {
+  if (object === null || typeof object !== "object" || Array.isArray(object)) {
+    throw new Error("contains requires an object");
+  }
+  return Object.hasOwn(object, property);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 719272787..c0b6104cc 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -24,17 +24,41 @@ as an array isn't an object
 // When passed to contains
 // Then it should return false
 test.todo("contains on empty object returns false");
+test("contains on empty object returns false", () => {
+  expect(contains({}, "name")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
-
+test("contains on an object with an existing property return ture", () => {
+  expect(contains({ name: "Cat", age: 10 }, "name")).toBe(true);
+});
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains on an object with a non-existent property return false", () => {
+  expect(contains({ name: "Ramesh", age: 23 }, "location")).toBe(false);
+});
 
 // Given a value that isn't an object - an array, a string, a number,
 // null, or no argument at all
 // When passed to contains
 // Then it should throw Error("contains requires an object")
 // (careful: typeof [] and typeof null are both "object")
+test("contains throws an error for a string", () => {
+  expect(() => contains("India", "0")).toThrow("contains requires an object");
+});
+test("contains throws an error for an array", () => {
+  expect(() => contains([1, 2, 3], "0")).toThrow("contains requires an object");
+});
+test("contains throws an error for null", () => {
+  expect(() => contains(null, "name")).toThrow("contains requires an object");
+});
+
+test("contains throws an error when no argument is given", () => {
+  expect(() => contains()).toThrow("contains requires an object");
+});
+test("contains throws an error for a number", () => {
+  expect(() => contains(100, "name")).toThrow("contains requires an object");
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..a859c918b 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,15 @@
-function createLookup() {
+function createLookup(pairs) {
   // implementation here
+  const lookup = {};
+
+  for (const pair of pairs) {
+    const countryCode = pair[0];
+    const currencyCode = pair[1];
+
+    lookup[countryCode] = currencyCode;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..f1de08c95 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -33,3 +33,12 @@ It should return:
    'CA': 'CAD'
  }
 */
+test("creates a country currency code lookup for multiple codes", () => {
+  const pairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+  const result = createLookup(pairs);
+
+  expect(result).toEqual({ US: "USD", CA: "CAD" });
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..f0ff3035d 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,32 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    if (!pair) {
+      continue;
+    }
+
+    const [key, ...rest] = pair.split("=");
+    const value = rest.join("=");
+
+    const decodedKey = decodeURIComponent(key.replace(/\+/g, " "));
+    const decodedValue = decodeURIComponent(value.replace(/\+/g, " "));
+
+    if (decodedKey in queryParams) {
+      if (Array.isArray(queryParams[decodedKey])) {
+        queryParams[decodedKey].push(decodedValue);
+      } else {
+        queryParams[decodedKey] = [queryParams[decodedKey], decodedValue];
+      }
+    } else {
+      queryParams[decodedKey] = decodedValue;
+    }
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..e9e0e9abd 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,7 +3,7 @@
 // Below are some test cases the implementation doesn't handle well.
 // Fix the implementation for these tests, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js");
 
 test("should parse values containing '='", () => {
   expect(parseQueryString("equation=a=b-2")).toEqual({
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..7fa4f1a06 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,26 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally requires an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    const key = String(item);
+
+    if (Object.prototype.hasOwnProperty.call(counts, key)) {
+      counts[key] += 1;
+    } else {
+      Object.defineProperty(counts, key, {
+        value: 1,
+        writable: true,
+        enumerable: true,
+        configurable: true,
+      });
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index ca763c296..bee676075 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -14,21 +14,80 @@ const tally = require("./tally.js");
  * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
  */
 
-// Acceptance criteria:
-
-// Given a function called tally
-// When passed an array of items
+// Given an array of items
+// When passed to tally
 // Then it should return an object containing the count for each unique item
+test("tally on a single item counts it once", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+});
+
+test("tally on repeated items counts each one", () => {
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+});
+
+test("tally on a mix of items counts each unique item", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts duplicates that are not next to each other", () => {
+  expect(tally(["a", "b", "a", "c", "b", "a"])).toEqual({ a: 3, b: 2, c: 1 });
+});
 
 // Given an invalid input like a string, a number, or no argument at all
 // When passed to tally
 // Then it should throw Error("tally requires an array")
+test("tally throws on a string", () => {
+  expect(() => tally("abc")).toThrow(new Error("tally requires an array"));
+});
+
+test("tally throws on a number", () => {
+  expect(() => tally(42)).toThrow(new Error("tally requires an array"));
+});
+
+test("tally throws when called with no argument", () => {
+  expect(() => tally()).toThrow(new Error("tally requires an array"));
+});
+
+test("tally throws on null, undefined and plain objects", () => {
+  expect(() => tally(null)).toThrow(new Error("tally requires an array"));
+  expect(() => tally(undefined)).toThrow(new Error("tally requires an array"));
+  expect(() => tally({ a: 1 })).toThrow(new Error("tally requires an array"));
+});
+
+// Extra edge cases
+test("tally handles item names that match built-in object properties", () => {
+  const result = tally(["constructor", "toString", "constructor"]);
+  expect(result.constructor).toBe(2);
+  expect(result.toString).toBe(1);
+});
+
+test("tally does not allow prototype pollution via __proto__", () => {
+  const result = tally(["__proto__", "__proto__"]);
+  expect({}.polluted).toBeUndefined();
+  expect(Object.keys(result)).toEqual(["__proto__"]);
+  expect(Object.getOwnPropertyDescriptor(result, "__proto__").value).toBe(2);
+});
+
+test("tally counts numbers and booleans by their string form", () => {
+  expect(tally([1, 1, 2, true, true])).toEqual({ 1: 2, 2: 1, true: 2 });
+});
+
+test("tally treats different cases as different items", () => {
+  expect(tally(["a", "A", "a"])).toEqual({ a: 2, A: 1 });
+});
+
+test("tally does not change the array it is given", () => {
+  const input = ["a", "b", "a"];
+  tally(input);
+  expect(input).toEqual(["a", "b", "a"]);
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..3dbe39a80 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,26 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    // it's the error
+    // invertedObj.key = value;
+    // fixed the code
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
+module.exports = invert;
 
 // a) What is the current return value when invert is called with { a : 1 }
-
+// ==>The return value when invert is called is "a":"1"
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
-
+// ==>The return value when invert is called are "a":"1", "b":"2"
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+// ==>The target return value when invert is called with{a:1, b: 2} are "1": "a", "2": "b"
 // c) What does Object.entries return? Why is it needed in this program?
-
+// ==>It turns an object into an array of [key, value] pairs. Object.entries({ a: 1, b: 2 }) gives [["a", 1], ["b", 2]]. It’s needed because a for...of loop can’t go through a plain object directly, and the function needs both the key and the value of each property. Object.entries provides both, and const [key, value] unpacks each pair.
 // d) Explain why the current return value is different from the target output
-
+// ==>first it used the dot notation instead of square bracket which is accessing the property using  a literal name
+// ==>second it is not inverted it still uses key value instead of value key so that it returns the inverted one.
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// ==>i have fixed the code and for testing i made the another file and make the edges cases.
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..fbe32fdc5
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,43 @@
+const invert = require("./invert.js");
+
+test("swaps keys and values for the example in the exercise", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+});
+
+test("works with a single key", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("works with two keys", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+test("returns an empty object for an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+test("string values become keys", () => {
+  expect(invert({ first: "one", second: "two" })).toEqual({
+    one: "first",
+    two: "second",
+  });
+});
+
+test("original numeric keys come back as strings", () => {
+  expect(invert({ 1: "a", 2: "b" })).toEqual({ a: "1", b: "2" });
+});
+
+test("when two keys share a value, the last key wins", () => {
+  expect(invert({ a: 1, b: 1 })).toEqual({ 1: "b" });
+});
+
+test("does not change the original object", () => {
+  const original = { a: 1, b: 2 };
+  invert(original);
+  expect(original).toEqual({ a: 1, b: 2 });
+});
+
+test("inverting twice gives back the original when values are unique strings", () => {
+  const original = { a: "x", b: "y" };
+  expect(invert(invert(original))).toEqual(original);
+});