Arrange the halogens F2, Cl2, Br2, I2, in order of their increasing reactivity with alkanes.

1. I2<Br2<Cl2<F2

2. Br2<Cl2<F2<I2

3. F2<Cl2<Br2<I2

4. Br2<I2<Cl2<F2

HINT- High electronegativity means high reactivity with alkanes
Alkane react with F2 is vigorously and with I2 the reaction is too slow that it requires a catalyst. It is because of high electronegativity of fluorine. Reactivity decreases with decrease in electronegativity and electronegativity decreases down the group.