Answer:
6.67%
Step-by-step explanation:
% by mass of hydrogen = mass of hydrogen/ total mass of the compound × 100%
mass of hydrogen = 1 × 12
= 12 g
total mass of compound = 12×6 + 1×12 +16×6
= 180 g
Therefore, % by mass of hydrogen = 12/180 × 100%
= 6.67%