There are different kinds of compositions. The percentage mass composition of chlorine is 42% in HClO3 (gram-formula mass = 84 g/mol)
This HClO3 is known to be popularly called as Chloric acid.
Percentage mass of chlorine is formula:
Percentage mass composition = mass of element * 100%/mass of compound.
Therefore;
HClO3 (gram-formula mass = 84 g/mol)
Percentage mass composition of chlorine = 35 * 100% / 84 = 42%
See full question below.
In which compound is the percent composition by mass of chlorine equal to 42%?
(1) HClO (gram-formula mass = 52 g/mol)
(2) HClO2 (gram-formula mass = 68 g/mol)
(3) HClO3 (gram-formula mass = 84 g/mol)
(4) HClO4 (gram-formula mass = 100. g/mol)
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