Option 2 : Equivalent

P, Q, R and S are statements such that if P is true, then Q is true and if P is false, then Q is false. The statements P and Q are **Equivalent.**

**Equivalent:**

- Two expressions are logically equivalent provided that they have the same truth value for all possible combinations of truth values for all variables appearing in the two expressions.
- The propositions are equal or logically equivalent when p and q are logically equivalent if p is true whenever q is true, and vice versa, and if p is false whenever q is false, and vice versa.
- If p and q are logically equivalent, we write p = q.

**Sub- contrary:** Propositions are subcontrary when it is impossible for both to be false although they may be true together. For example “some lunches are free” is false, “some lunches are not free” must be true.

**Contradictory:** In traditional logic, a contradiction consists of a logical incompatibility or incongruity between two or more propositions. It occurs when the propositions, taken together, yield two conclusions that form the logical, usually opposite inversions of each other. Thus if P is true then F has to be False.