7. Which of the following element shows the same reactivity as Chlorine? a. Fluorine
C. Magnesium
b. Sodium
d. Sulfur

Chlorine, bromine and iodine react with hot iron to produce a brown solid. Hence, chlorine, bromine and iodine exhibit similar chemical properties. The observations also show that the reactivity of the halogens in their reactions with iron decreases from chlorine → bromine → iodine.

Explanation:

not sure if this will help

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume