Which of the following statements are so related that they cannot both be true, nor can they both be false? Choose the correct answer from the options given below.

1.All mammals are vertebrates

2.Some mammals are vertebrates

3.Some mammals are not vertebrates

4.No mammals are vertebrates

A1 and 2 only

B2 and 4 only ✓ Correct

C3 and 4 only

D1 and 4 only

Correct answer: (B) 2 and 4 only

Explanation

'Some mammals are vertebrates' and 'No mammals are vertebrates' cannot both be true nor both false.

That exact condition defines the relation of contradiction.

These two are an I proposition and an E proposition.

On the square of opposition I and E are contradictories.

Exactly one of them must be true and the other false.

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