What is the correct answer the yolk of egg is white or the yolk of egg are white?

Answer 1

First both would be wrong because the yolk of an egg is in fact yellow not white!

However, on the point of grammar, the yolk of an egg is a singular object and therefore the correct declination of the verb to be in the sentence would be 'is' and not 'are'.

Thus the proper form is 'the yolk of the egg is yellow' and for the plural case 'the yolks of the eggs are yellow'

Answer 2

First, and foremost, the yolk is yellow, and either expression may be correct depending on whether you are speaking of one yolk or many.