(p∧~q)∧(~p∧q) is
a tautology
a contradiction
both a tautology and a contradiction
neither a tautology nor a contradiction
(p∧~q)∧(~p∧q)=(p∧~p)∧(~q∧q)=f∧f=f
(by using associative laws and commutative laws)
∴ (p∧~q)∧(~p∧q) is a contradiction.