Aheavy 2.0kg ball is moving at 10m/s when it is caught. a light 1.5kilogram ball is travelling at 20m/s when it caught. which ball required the greater impulse?

To count impulse you will need more information as it was different with time. In this question, there are two balls with different mass and velocity, thus they have different momentum. I will assume you are asking about the momentum

The momentum of ball 1 should be:
momentum 1= mass1 * velocity1
momentum 1= 2kg * 10m/s= 20kg m/s

The momentum of ball 2 should be:
momentum 2= mass2 * velocity2
momentum 2= 1.5kg * 20 m/s= 30kg m/s

The answer would be: 1.5kg ball because it was travelling faster