diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..7368f1e13 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,10 @@
 // Predict and explain first...
+/*
+Objects don't use indexes like arrays. If we try to access address[0], it returns undefined because address
+is an object, not an array. Objects store values using keys (property names). To retrieve a value, we can use
+either dot notation, such as address.houseNumber, or bracket notation, such as address["houseNumber"].
 
+*/
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +17,4 @@ 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..87eea84cf 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,8 +1,14 @@
 // Predict and explain first...
-
+/* 
+author is an object. The original code tries to use a for...of loop directly on the object, but normal objects 
+cannot be directly iterated using for...of. Since we only want the property values, we can use Object.values(author) 
+to get all the values from the object.
+ */
 // 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
 
+
+
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -10,7 +16,5 @@ const author = {
   age: 40,
   alive: true,
 };
+console.log(Object.values(author));
 
-for (const value of author) {
-  console.log(value);
-}
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..081d1993e 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,5 +1,9 @@
 // Predict and explain first...
-
+/*
+The printing of title and serves is absolutely correct, but to print ingredients on a new line isn't correct. 
+To retrieve values, we use Object.values(recipe). To print ${recipe} isn't the right way. We can use a for...of 
+loop to print each ingredient on a new line.
+*/
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
 // How can you fix it?
@@ -10,6 +14,7 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}`);
+for(let values of Object.values(recipe.ingredients)){
+  console.log(values);
+}
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..0ed225476 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,14 @@
-function contains() {}
+function contains(obj, item) {
+    if (typeof obj !== "object" || obj === null || Array.isArray(obj)){
+        return false;
+    }
+    let getKey = Object.keys(obj);
+    for (let element of getKey){
+        if(element === item){
+            return true
+        }
+    }
+    return false;
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..1edce369b 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -11,25 +11,37 @@ E.g. contains({a: 1, b: 2}, 'c') // returns false
 as the object doesn't contains a key of 'c'
 */
 
-// Acceptance criteria:
-
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test("return true if object's property exists otherwise false", () => {
+    expect(contains({name: "maryam", city: "Derby"}, "city")).toBe(true);
+});
 
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("return false if object is empty", () => {
+    expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("return true if object's property contains the property", () => {
+    expect(contains({name: "maryam", city: "Derby"}, "city")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("return false if property is non-existent", () => {
+    expect(contains({name: "maryam", city: "Derby"}, "age")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("return false if it's not an object", () => {
+    expect(contains([], 6)).toBe(false);
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..d826d656e 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,7 @@
-function createLookup() {
+function createLookup(arr) {
   // implementation here
+  const obj = Object.fromEntries(arr);
+  return obj;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..66d85f7a5 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,19 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () =>{
+  expect(createLookup([['US', 'USD'], ['CA', 'CAD'], ['PAK', 'PKR'], ['SAUDI', 'RIYAL']])).toEqual({
+   'US': 'USD',
+   'CA': 'CAD',
+   'PAK' : 'PKR',
+   'SAUDI' : 'RIYAL'
+ });
+});
+test("the array is empty", () =>{
+  expect(createLookup([])).toEqual({});
+});
+test("creates a country currency code lookup for single code", () =>{
+  expect(createLookup([['Uk','POUND']])).toEqual({'Uk': 'POUND'});
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..cca92c87c 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,16 +1,48 @@
 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 checkSeparator = pair.indexOf("=");
+
+    let key;
+    let value;
+
+    if (checkSeparator === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, checkSeparator);
+      value = pair.slice(checkSeparator + 1);
+    }
+
+    key = key.replace(/\+/g, " ");
+    value = value.replace(/\+/g, " ");
+
+    key = decodeURIComponent(key);
+    value = decodeURIComponent(value);
+
+    if (Object.prototype.hasOwnProperty.call(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;
\ No newline at end of file
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..cb2d42012 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -46,3 +46,33 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+// Multiple normal key-value pairs
+test("should parse multiple key-value pairs", () => {
+  expect(parseQueryString("name=Maryam&age=25")).toEqual({
+    name: "Maryam",
+    age: "25",
+  });
+});
+
+test("should return empty object for empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("should replace multiple '+' characters with spaces", () => {
+  expect(parseQueryString("name=John+Michael+Doe")).toEqual({
+    name: "John Michael Doe",
+  });
+});
+
+test("should decode encoded keys and values", () => {
+  expect(parseQueryString("hello%20world=good%20morning")).toEqual({
+    "hello world": "good morning",
+  });
+});
+
+test("should ignore multiple empty key-value pairs", () => {
+  expect(parseQueryString("name=Maryam&&&age=25&&&")).toEqual({
+    name: "Maryam",
+    age: "25",
+  });
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..e4db6c1ef 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,14 @@
-function tally() {}
-
+function tally(arr) {
+    const result = arr.reduce((obj, item) => {
+        if (obj [item]) {
+            obj[item] = obj[item] + 1;
+        }
+        else{
+            obj[item] = 1;
+        }
+        return obj; 
+    }, {});
+    
+    return result;
+}
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..1a88bb231 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,52 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("when an array is passed, it should return an object containing the count for each unique item", () => {
+  expect(tally(["banana", "apple", "cherry", "apple", "cherry"])).toEqual({
+    banana: 1,
+    apple: 2,
+    cherry: 2
+  });
+});
 
 // 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("should return the count for duplicate items", () => {
+  expect(tally(["apple", "apple", "apple", "banana"])).toEqual({
+    apple: 3,
+    banana: 1
+  });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("should throw an error when passed a string", () => {
+  expect(() => tally("apple")).toThrow();
+});
+
+// Case: array containing numbers
+test("should count occurrences of numbers", () => {
+  expect(tally([1, 2, 2, 3, 3, 3])).toEqual({
+    1: 1,
+    2: 2,
+    3: 3
+  });
+});
+
+// Case: array containing mixed data types
+test("should count occurrences of mixed items", () => {
+  expect(tally(["apple", 1, "apple", 1, "banana"])).toEqual({
+    apple: 2,
+    1: 2,
+    banana: 1
+  });
+});
\ No newline at end of file
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..249c86257 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,40 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj.key = value; // key 1
   }
 
   return invertedObj;
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+// {key : 1}
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// {key ; 2}
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// {1 : "a", 2 : "b"}
 
 // c) What does Object.entries return? Why is it needed in this program?
+// It returns all the key-value pairs of an object. We need it to get both the keys and values.
 
 // d) Explain why the current return value is different from the target output
+/*Because we are not swapping it correctly. We haven't handled the key correctly,
+ so it's giving us the "key" keyword, not the way we need it.
+ Plus, we aren't storing each value correctly, so the previous value gets overwritten
+ when there are multiple values.*/
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+//e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+const obj = {x : 10, y : 20};
+console.log(invert(obj));
\ No newline at end of file