What is the percent composition of hydrogen in a compound if the mass of the initial compound is 276 grams and the mass of collected hydrogen after decomposition is 41.4 grams?

a.
6.6%
b.
10.0%
c.
15.0%
d.
21.2%

If 3 moles of a compound use 24 j of energy in a reaction, what is the a hreaction in j/mol?

Is hydrogen gas a reactant or product

When studying the halogens (group 17) on the periodic table, how does the number of the valence electrons change as the energy level is increased? a) the total number of valence electrons does not change, it remains 7. b) the total number of valence electrons does not change, it remains 1. c) the total number of valence electrons increases by 1 with each energy level. d) the total number of valence electrons decreases by 1 with each energy level.