Read the given statements and conclusions carefully. You have to take the given statements to be true even if they seem to be at variance from commonly known facts. You have to decide which conclusion(s) logically follow(s) from the given statements Statements: No river is a mountain. Some rivers are animals. Some birds are mountains. Conclusions: I: No animal is a mountain. II: No river is a bird.

Correct — B. A conclusion follows only if it holds in every diagram consistent with the statements, so a single counter-diagram kills it.

I — "No animal is a mountain": only the animals that are also rivers are barred from being mountains. Animals outside the river circle are unconstrained, so one of them may be a mountain. I fails.

II — "No river is a bird": only the birds that are mountains are barred from being rivers. The other birds are free, so a river may still be a bird. II fails.

Neither follows → option (b).

Why the others are wrong

• (a)
  Both conclusions (I) and (II) follow — Both conclusions are universal negatives, and the statements forbid neither overlap. A definite "no" must hold in every consistent diagram; here one counter-diagram already breaks each of them.
• (c)
  Only conclusion (I) follows — Conclusion I overreaches. Only the animals that are also rivers are pushed out of mountains; the animals lying outside the river circle carry no restriction at all.
• (d)
  Only conclusion (II) follows — Conclusion II overreaches. Only the birds that are mountains are pushed out of rivers; the remaining birds are unrestricted, so a river may still be a bird.

A particular affirmative — "Some A are B" — describes part of A and says nothing whatever about the rest.

So it can never support a universal negative about all of A. The most "No river is a mountain" plus "Some rivers are animals" will give you is the particular "Some animals are not mountains".

Test a conclusion by trying to build one diagram in which the statements are true and the conclusion is false. If you can build it, the conclusion does not follow.

Key facts

• "No river is a mountain" + "Some rivers are animals" yields only "Some animals are not mountains".
• "No river is a mountain" + "Some birds are mountains" yields only "Some birds are not rivers".
• One valid counter-diagram is enough to reject a conclusion.

Common traps

• Assuming that because rivers and mountains are disjoint, everything linked to rivers is disjoint from mountains too.
• Reading "Some rivers are animals" as though it described all animals.
• Importing real-world knowledge that rivers and birds are different kinds of thing — the stem tells you to take the statements as true regardless.

No directly related past PYQ was found.