How many neutrons are there in 9 molecules of 31 p4

Atomic weight of P = 31 g/mol
Molecular weight of P4 = 31*4 = 124 g/mol

You have 31 g of P4, so we can find how many moles of P4 you have:
31 g P4 divided by 124 g/mol P4 = 0.25 moles.

Now we have to multiply the number of moles (0.25) with Avogadros number:
0.25 mol * 6.022 x 10²³ molecules/mol = 1.5055 x 10²³ molecules of P4

P4 consists of four P, and each P has 15 neutrons (because it is number 15 in the periodic table)

1.5055 * 10²³ * 4 * 15 = 9.033 x 10^24 

Since it's has nine molecules, you need to multiply this by 916×9 = 144 hope this helps

Ibelieve its a because an empirical formula usually has a ch in it your options are a or b