What trend in metallic reactivity is found going left to right on periodic table of elements

What is the number of neutrons in an atom with atomic mass of 35

How does a sample of helium at 15 degree celsius compare to a sample of helium at 215 k? a) the helium at 15 degrees celsius has a higher average kinetic energy that the sample at 215 k. b) the helium at 15 degrees celsius has lower nuclear energy that the sample at 215 k. c) the helium at 15 degrees celsius has slower- moving atoms that the sample at 215 k. d) the helium at 15 degrees celsius has smaller atoms than the sample at 215 k.

Stoichiometry- i need with 14 and 15! an explanation would be appreciated!