I thought these were easy but got confused when I had to solve for the ? mark?

Question

a) 235 top 92 bottom U --> 87^ 35 Br + ? + 1^ 0n

b) 250^ 98 Cf + 11^ 5B --> ? + 4in front of 1up 0down n

c) Positron emission of Ba--125

I am so ...HELP!

Answer 1

(a) 235 - U - 92 = 87 - Br - 35 + X + 1 - n - 0

The mass numbers must balance, so the mass number of X must be 235 - 87 - 1 = 147

The proton numbers must balance, so the proton number of X must be 92 - 35 = 57

So X must be 147 - La - 57.

(b) 250 - Cf - 98 + 11 - B - 5 = X + 4 1 - n - 0

The mass number is 250 + 11 - 4 = 257

The proton number is 98 + 5 = 103

So the unknown is 257 - Lr - 103

(c) 125 - Ba - 56 = X + positron

Positron emission results when a proton is transmuted into a neutron, so X is 125 - Cs - 55