Answer : The coefficient placed in front of NaCl to balance this equation should be, 2
Explanation :
Balanced chemical reaction : It is defined as the reaction in which the number of different atoms of elements present in reactant side must be equal to the number of different atoms of elements present in product side.
The given unbalanced chemical reaction is,

The given balanced chemical reaction will be,

By the stoichiometry we can say that, 1 mole barium chloride react with 1 mole of sodium carbonate to give 1 mole of barium carbonate and 2 moles of sodium chloride.
Hence, the coefficient placed in front of NaCl to balance this equation should be, 2