Question

explain :-


group 17 elements are strong non-metals, while group 1 elements are strong metal

halogen have a high electron affinity

Answer 1

Because group 17 elements have 7 electrons in their last class but they have to gain 1 electron to complete their class that they have high electron affinity but group 1 have only 1 electron in their last class that they can loose it easily.

Answer 2

Group 17 elements are strong non metals because they need to gain one more electron to get their octet. Since gaining electrons means a negative charge, they are considered as strong non metals.
Group 1 elements are strong metals because they need to lose one more electron to get their octet. Since losing electrons means a positive charge, they are considered as strong metals.

Halogens have high electron affinity because of the less number of electrons present in the outer most shell and they are placed far from the nucleus to decrease the pull from the nucleus.
Hope it helps you