Three of the following four number-pairs are alike in a certain way and one is different. Find the odd one out.

25 : 676 $$\longrightarrow\ $$ 25 : 26$$^2$$ $$\longrightarrow\ $$ 25 : (25+1)$$^2$$

21 : 484 $$\longrightarrow\ $$ 21 : 22$$^2$$ $$\longrightarrow\ $$ 21 : (21+1)$$^2$$

24 : 529 $$\longrightarrow\ $$ 24 : 23$$^2$$ $$\longrightarrow\ $$ 24 : (24-1)$$^2$$

30 : 961 $$\longrightarrow\ $$ 30 : 31$$^2$$ $$\longrightarrow\ $$ 30 : (30+1)$$^2$$

Every Option is in the form of N : (N+1)$$^2$$ except Option C

Hence, the correct answer is Option C