Select the number-pair in which the two numbers are related in the same way as are the two numbers of the following number-pair.
442 : 21

we know that the square of 21 is 441 and the ratio given is in similar way with just a slight difference of +1 

the similarly format is followed by 257 and 16 where 256 is the square of 16 and adding 1 to it makes it 257

where as square of 13 is 169

                                14 is 196

                                19 is 361 

non of them have the similar format except the first option

so the correct answer is $$16^{2}$$ +1 =257