Question

balance barium chloride + sodium sulphate. give step by step

Answer 1

Barium chloride → BaCl2
Sodium sulphate → Na2SO4

So
BaCl2 + Na2SO4 → NaCl + BaSO4
To balance it
Let a molecules of BaCl2 and b molecules of Na2SO4 and c molecules of NaCl and d molecules of BaSO4

Therefore 
a BaCl2 + b Na2SO4 → c NaCl + d BaSO4
     
Reactants side            →       products side
Ba = a                                      Ba = d
Cl  = 2a                                   Cl = c
Na = 2b                                   Na = c
S    = b                                     S  = d
O = 4d                                     O = 4d     

Therefore
a = d
2a = c
b = d
4d = 4d

Let a = 1 then d = 1

2a = c ⇒ c = 2
d = b = 1

a = 1, b = 1, c = 2, d = 1
Now substitute these values in equation
BaCl2 + Na2SO4 → 2 NaCl + BaSO4
This is the balanced equation.

This is a new process of solving equations.   
Hope you understand and it helps you  ^_^