If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Find the missing number in the image below.

You are provided with a grid (as shown in the picture). Can you fill the squares with numbers 1-8 in a manner that none of the two consecutive numbers are placed next to each other in any direction (vertically, horizontally or diagonally?)

What work can one never finish?

What animal walks on four legs in the morning, two legs during the day, and three legs in the evening?

Oedipus, the king of Thebes, figured out the answer to the riddle:

Why is it very easy to weigh a fish?

Find the Goldfish below the given Image.

I am a type of word that is spelt incorrectly or used differently, on purpose for humour. What am I?
Hint 1: You can find me in a joke.
Hint 2: I am a play on words.

Which country gets ill every time?

What do you call a fish without an eye?