Its a bit of a weird question ish for (ii) but the way that you approach it is that you know that the Water formula is H20 and the question says that 0.2 mol of water is produced and also you know the relative atomic mass for Hydrogen=1, You also know the relative molecular mass of H2O =18 so, if you form a ratio with that you know that 2/18=H/0.2 and therefore with rearrangement H=0.022 mol to 2 sig figs

For part iii You know that when a hydrocarbon burns (aka complete combustion) all of its carbon turns to carbon dioxide and all of its hydrogen turns to water.

so basically if you kinda convert what you know and don't know in terms of numbers for the chemical equations u kinda get something like this CxHy + nO2 --> xCO2 + 0.5yH2O

As a result how ever many times the volume of carbon dioxide is of the hydrocarbon, that is the number of carbon atoms.

In this case the mol of the hydrocarbon = 0.05 mol of carbon dioxide = 0.2 and the number of carbon atoms in the hydrocarbon = 0.2/0.05 = 4

Hope that made a bit of sense excuse my terrible formatting tho lol