Hello,

I'll explain you two difference between alkali metal and halogens below-

1. Alkali metals are soft and reactive metals. They react vigorously with water and become more reactive. And other hand halogens are reactive non metals.

2. Alkali metals are all solid and the melting point decrease as they get bigger. Halogens can be solid, liquid, gaseous at room temperature and the melting point increase when they get bigger.

All the best.