Question

How many neutrons are there in 9 molecules of P4 with mass number 31 and proton number 15?

Answer 1

A = mass number which is equal to the total number of protons + number of neutrons, Z= atomic number of any element which is also indicates Number of protons or number of electron in the given atom.

The formula to calculate neutron would be :

mass number - proton  

31   - 15     = 16

Thus 16 neutrons are found in one atom of P  

There are 4 atom in one molecule

Thus  

4 atom /1 molecule * 9 molecule * 16 neutron / 1 atom  

= 4*9*16= 576 neutrons

Answer 2

The formula to calculate neutron would be :

mass number - proton 

31   - 15     = 16

Since it got 9 molecules, you need to multiply this by 9 , 

16 x 9  = 144

hope this helps