Which of the following propositions are so related that they can neither be true together nor they be false together?

1.All printers are computer peripherals.

2.Some computer peripherals are printers.

3.Some printers are not computer peripherals.

4.No printers are computer peripherals.

A1 & 4 only

B2 & 3 only

C1 & 3 only ✓ Correct

D1 & 2 only

Correct answer: (C) 1 & 3 only

Explanation

Statements 1 and 3 can neither be true together nor false together.

Statement 1, 'All printers are computer peripherals', is a universal affirmative.

Statement 3, 'Some printers are not computer peripherals', is its matching particular negative.

A universal affirmative and its particular negative are contradictories, so exactly one of them must be true.

Statement 2 is only the converse of a related affirmative and Statement 4 is the contrary, neither giving strict contradiction.

Thus the contradictory pair is the first and the third.

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