Answer
Please see the work below.
Work Step by Step
(a) A pale yellow gas that reacts with water - Fluorine ($F_{2}$).
Fluorine reacts with water to form $HF$ and $O_{2(g)}$
(b) A soft metal that reacts with water to produce hydrogen - Sodium (Na).
Sodium is a soft metal; it reacts vigorously with water to form $NaOH$ and $H_{2}(g)$.
(c) A metalloid that is hard and has a high melting point - Boron (B).
Boron is a metalloid; it is a dark crystalline hard substance with a melting point of $2000 ^{\circ}C$.
(d) A colorless, odorless gas - Nitrogen ($N_{2}$)
Nitrogen is a colorless odorless gas.
(d) A metal that is more reactive than iron, but does not corrode in the air - Aluminum (Al)
Aluminum is a metal that displaces iron from its solution. But it does not corrode in the air due to the formation of a thin oxide layer.
