Question

Please help me out!!!

Answer 1

What subject is this ?

Answer 2

Normally these questions ask for the empirical formula of the compound. You want mass%, so you get mass%:
Mass C in 7.93mg CO2
Molar mass CO2 = 12.011+15.999*2 = 44.009g/mol
Molar mass C = 12.011
Mass C = 12.011/44.009*7.93 = 2.1643mg C

Mass H in 4.87mg H2O
Molar mass H2O = 1.008*2+15.999 = 18.015g/mol
Molar mass H2 = 1.008*2 = 2.016
Mass H in 4.87mg H2O = 2.016/18.015*4.87 = 0.545mg H

Mass O = 5.59 -(2.1643 + 0.545) = 2.8807mg

% mass composition:
C = 2.1643/5.59*100 = 38.71%
H = 0.545/5.59*100 = 9.750%
O = 2.880/5.59*100 = 51.52%