Mole

[ally1784]

Guys, why is part a 5 and part b 2.5
n = m/M

[Sine]

Guys, why is part a 5 and part b 2.5
n = m/M

I think you need to consider an alternative formula for n

n = N/Na

where
n = moles
N = number of particles (e.g. particles of H2)
Na = avagadro's constant which is 6.02 x 10^23

Edit: misread the q (didnt see the "in mol" part. See below for the correct answer.

[Bri MT]

A H2 molecule has twice the mass of one H atom.

You then do:
n(H2) = m/M = 5/2 = 2.5   and n(H) = m/M = 5/1 = 5


Hope this helps

[ally1784]

How do I know that I'm looking for just one H atom (part a) because at the start I thought I was looking for H2, and that's how I got the answer 2.5?

[Chocolatepistachio]

Part a it’s H2 so you just do n=m/M and then x the answer by 2 because there are 2 atoms of H . B it’s just H so you don’t need to x 2

[ally1784]

how do I solve this?

[Bri MT]

how do I solve this?

First you find the number of mols using n=m/M
Get M from the periodic table.

Then you use n*Na = N   (look at Sine's post)