Hi!
The correct option would be A.
This is because the displacement reaction would take place as follows
Ca + ZnCl2 --> CaCl2 + Zn
A displacement reaction is one in which a substitution occurs, as the more reactive element in the mixture replaces one that is less reactive.
In the electrochemical series, we find Ca higher than Zn, which is indicative of Ca being more reactive, and having the capacity to displace Zn to form a compound.
Option D would be incorrect as no such substitution occurs.
Option B would be incorrect because again, there is no substitution occurring, and also because two metals alone (Ca and Zn in our case) can never react to form a compound.
Option C would be incorrect because it is not possible because CaCl and ZnCl are forms that are too unstable to exist due to an overall positive charge.
Hope this helps!
