Question

please clear this thing where we gave to use
(2Ag + Br2)

Answer 1

The numbers are used to balance the no. of atoms on both sides of the equation. According to law of conservation of mass, sum of mass of reactants is equal to sum of mass of products, i.e., the no. of atoms must be the same.

LHS = Ag has 2 atoms and Br has 2

similarly,

RHS = Ag has 2 atoms and Br has 2.