The given sets are as follows:

**{S(x,Ram),S(y,Sita)}****{P(x,y),P(f(x),z),P(z,x)}**

There are three conditions for unification of two sets:

Predicate symbol must be the same.

Number of arguments in both statements must be identical.

If two similar variables are present in the SAME expression, then unification fails.

The first set is non-unifiable because constants can never be unified.

In the second sentence, if we try to go for unification, we will end up with unifying x/f(x) which goes against the third rule. Hence, unification fails.

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