Answer: The coefficient in front of sodium hydroxide is 2.
Step-by-step explanation:
A double displacement reaction is one in which exchange of ions take place. The salts which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.
the balanced reaction between sodium hydroxide and copper (II) sulphate is :

Thus the coefficient in front of sodium hydroxide is 2.