Calculate the number of hydrogen and carbon present in 4g of methane

I'm going to do it by stoichiometry :

molar mass of CH4 is 16

and there are 4 H atoms in each CH4 so one mole CH4 consists of 4 x 6.022x10^23 H atoms

so :

4gr CH4 x (1mole CH4 /16 gr CH4) x (4 x 6.022 x 10^23 H atoms/1mole CH4) =

=6.022 x 10^23 H atoms

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6