Boyle's law is valid only when: MCQ with Answer and Explanation

Explanation:
Distilled water is considered the purest form of water because it is obtained by boiling water and condensing the steam, leaving almost all impurities, minerals, and salts behind. Rainwater is relatively pure but dissolves atmospheric gases and dust as it falls.

Explanation:
Magnesium reacts with hot water or steam to form MgO/Mg(OH)₂ and H₂, but very slowly with cold water (thin layer of insoluble hydroxide inhibits reaction). Sodium, potassium, and calcium react vigorously with cold water. Aluminium, zinc, iron react with steam but not cold water. Reactivity with water follows the series: K, Na, Ca (cold water); Mg, Al, Zn, Fe (steam).

Explanation:
Hydrogen is considered the cleanest fuel because its combustion produces only water (2H₂ + O₂ → 2H₂O) and no greenhouse gases or toxic pollutants. Coal, wood, and diesel produce CO₂, CO, SO₂, and particulate matter, contributing significantly to air pollution and global warming.