Verbal Reasoning - Mental Ability Questions

A is the son of B and D is the son of the sister of B. So, A is the cousin of D. 

Oxygen helps in burnings while carbon dioxide extinguished fires.

Hence, Oxygen : Burn :: Carbon dioxide : Extinguish.

It is irrelavent

PSRQ --> {16, 19, 18, 17} - next 3 alphabets of "P" is written in reverse order
SVUT --> {19, 22, 21, 20} - next 3 alphabets of "S" is written in reverse order

MNPO --> {13, 14, 16, 15}

KNML --> {11, 14, 13, 12} - next 3 alphabets of "K" is written in reverse order

Except "MNPO", others are not in consecutive order.

4 is father of 1 and grandfather of 6. So, 1 is father of 6. Thus, 4 and 1 are the two fathers.
3 is the sister of 6. So, 3 is the daughter of 1. Since there is only one mother, it is evident that 5 is the wife of 1 and hence the mother of  3 and 6. So, 2 is brother of 1. There are three brothers. So, 6 is the brother of 3. Hence, 2 and 1 are brothers. 6 is the brother of 3. So, three brothers are 1, 2, 6.

Word is divided into groups of two letters each and then letters of each group move one place forward and one place backward alternatively as in English alphabet. Hence, 

PERINATH => PE RI NA TH =>QFQHOBSG  and POLE => PO LE => QPKD

similarly,

SYNDROME => SY ND RO ME => TZMCSPLD

Clearly, the required number would be such that it leaves a remainder of 1 when divided by 3, 4, 5, or 6 and no remainder when divided by 7. Thus, the number must be of the form (L.C.M of 3, 4, 5, 6) x + 1 i.e., (60x + 1 ) and a multiple of 7. Clearly, for x = 5, the number is a multiple of 7. So the number is 301.