We can find it by 2n^2 formula
So
First shell is maximum of 2
Second shell is of 8
Third shell is of 18
Fourth shell is of 32
What are the following options?
If you mix Ammonia as well as Hydrogen chloride, you will get ammonium chloride. It is given by NH3 (g) + HCl (g) → NH4Cl(s).
Answer:

------->
+ 

Explanation:
In equation 1, equating the mass number (A) on both sides.
A = 235 + 1 = A + 94 + 3*1
236 = A + 94 + 3
A = 236 - 94 = 3
A = 139
Equate the atomic numbers on both sides
92 + 0 = Z + 36 + 3*0
92 = Z + 36
Z = 92 - 36
Z = 56
In reaction 2, equating the mass number on both sides
235 + 1 = A + 143 + 3 *1
236 = A + 143 + 3
236 = Z + 146
Z = 90
Equatoing the atomic number of both sides
92 + 0 = Z + 54 + 3*0
92 = Z + 54
Z = 92 - 54
Z = 38.