Mark the right statement:
(i) Coprime numbers must be both prime always.
(ii) Of two coprime numbers one is prime and the other is composite always.
(iii) Coprime numbers are twin primes.
(iv) Two consecutive integers are always coprime.

Let consider two numbers 3 & 8 ,they are coprime to eachother but 8 is not prime number.

So, Statement: (i) Coprime numbers must be both prime always, is not valid.

Let consider two numbers 2 and 3 ,they are coprime to eachother but none of them are composite number.

So, Statement: (ii) Of two coprime numbers one is prime and the other is composite always, is also not valid.

17 &  26 are also coprime to eachother but they are not twin prime.

So, Statement: (iii) Coprime numbers are twin primes, is not valid.

But if we consider any two consecutive numbers ,they are always coprime,as they create even,odd pair for any two number set.

So, Statement (iv) is valid only.

B is correct choice.