How far apart does corn seeds need to be apart to grow?

ALMOST

well it depends on the seed. like if you plant corn it has to be 8-12 in. apart or you can just look on the back of the seed packet.

far enough for them to grow idiot why do you care? plant them .00001 inches apart and see what happens

You can plant 3 or 4 seeds an inch apart (a 'Hill')in the hopes that one of them, at least, will germinate and grow. The hills should be 4 to 7 feet apart, depending on the type of watermelon.