In the formula, ch4, the percent composition of all elements is:
a. 75% c, 25% h
b. 25% c, 75% h
c. 81% c, 19% h
d. 20% c, 80% h

The problem is not clear if the percent composition is in terms of mole or mass. I will just present the two.

For mole percent.

Total number of moles of element per mole CH4 = 1 mol C + 4 mol H = 5 mol

therefore we have
% mol C = 20%
% mol H = 80%

for mass percent'

Molar mass of CH4 = 16 g/mol
 molar mass of C = 12
molar mass of H = 4*1 =4

thus
% mass C = 12/16 = 75%
% mass H = 4/16 = 25%

both answers are in the choices but percent composition is usually expressed in mass therefore I think choice A would be the best answer. 

The atomic nucleus made up from protons (yellow) and neutrons (blue) and held together by nuclear forces. nuclear forces (also known as nuclear interactions or strong forces) are the forces that act between two or more nucleons. they bind protons and neutrons (“nucleons”) into atomic