What is wrong with my code? C# beginner

Hi there, I am trying to create a game in where an object in unity rotates 90 degrees when the mouse is clicked. I have made it so that the object moves to the right as can be seen in the code below. So I tried to write a similar bit of code for this rotation script but it's not working for me. Can anybody please tell me where I have gone wrong? Thanks!

using UnityEngine; using System.Collections;

public class Movement : MonoBehaviour {

 // Use this for initialization
 void Start()
 {}

 // Update is called once per frame
 void Update () {

     Rigidbody2D rb = GetComponent<Rigidbody2D>();
     // Change the mass of the object's Rigidbody.
     rb.mass = 10f;
     rb.AddForce(Vector2.right * 10f);

 }

}

public class Rotate : MonoBehaviour { void OnMouseDown()
{

     Rigidbody2D rb = GetComponent<Rigidbody2D>();
     // Rotate the object's Rigidbody.
     rb.transform.Rotate(new Vector3( 0, 90, 0));

 }
 }