Iodine is used to test the presence of ___________ in

Select the missing number from the given responses:

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

 First row: 84, 42, 49

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

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

JRH : ? : : KOV : 51 

Find the missing numbers.

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

4, 21, 86, 261, 526, ?

 Find the missing number. 

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