Answer:
Alkali Metals: •are placed in group 1, • can be cut with a knife
Halogens: •are placed in group 17, • react vigorously with metals
Explanation:
Alkali metals are the metals found in group 1 of the periodic table. They have one outermost shell electron. They react with cold water vigorously to form alkalis and liberate hydrogen gas as well. They are very reactive metals and their reactivity increases on going down the group. They are soft and can be cut with a knife. Examples of alkali metals are lithium, sodium,potassium, rubidium,caesium, francium.
The Halogens are reactive non-metals placed in group 17 of the periodic table. They have seven outermost shell electrons. They are the most reactive non-metals react vigorously with metals by to form ionic compounds. They exist as diatomic molecules. They are found in nature mainly as salts because of their reactivity. Their reactivity decreases on going down the group. Examples of the halogens include fluorine, chlorine, bromine, iodine and astatine.
