Why a golf ball is heavier than a table-tennis ball

The balls have the same mass but the table-twnnis ball is much less dense then the golf ball.

since a table tennis ball is hollow and made of plastic compared to a golf ball which is solid and made from a harder substance so it can withstand the gold clubs hit

Two events are mutually exclusive if they cannot occur at the same time.
So, I would go with A.

examples :
turning left and turning right are mutually exclusive because u cant do both at the same time.
tossing a coin, picking heads and picking tails are mutually exclusive.