The percent composition of all elements in hclo3 is:
a. 2% h, 20% cl, 78% o
b. 1% h, 42% cl, 57% o
c. 2% h, 68% cl, 30% o
d. none of the above

The percent composition is defined by mass percent. So the calculation is through the atomic mass. The mass for H is 1, Cl is 35.5, O is 16. So the answer is B.

The number of protons in a nucleus

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts