We can compare two objects using the words lighter or heavier. The elephant is heavier than the mouse. The mouse is lighter than the elephant.
Which animal is heavier, the cat or the horse? The cat is lighter than the horse. The horse is heavier than the cat. The animal which is heavier is the horse.
Which is lighter, the apple or the watermelon? The apple is lighter than the watermelon. The watermelon is heavier than the apple.
We compared two objects using the words lighter or heavier. The horse was heavier and the apple was lighter.