What is the main component of natural gas?

What number should replace the question mark? 

In each of the following questions select the related letter/word/figure/number from the given alternatives.

JRH : ? : : KOV : 51 

Select the number from among the given option that can replace the question mark (?) in the following series.

6, 31, 126, 381, 766, ?

Study the given pattern carefully and select the number that can replace the question mark (?) in it.

First row: 14, 12, 108

Find the missing number?

What will come in the place of question mark?

Select the number from the given option that can replace the question mark (?) in the following series:

32, 16, 24, 60, ?, 945

Study the given matric carefully and select the number from among the given options that can replace the question mark (?) in it.

Select the option that is related to the third number in the same way as the second number is related to the first number.

15 : 5 :: 26 : (?)

Find the missing number by analysing the pattern followed by the numbers in each row.