Answer:
C = 13.64%
F = 86.36%
Explanation:
Percentage composition = (mass/molar mass) x 100
Molar mass of CF4 = 88
C = 12g/mol
F = 19g/mol
C = 12/88 x 100 = 13.64%
F = 76/88 x 100 = 86.36%