The freezing point of mercury is -39°C. It cannot be used in thermometers for temperatures below this because MCQ with Answer and Explanation

Explanation:
Rocket propulsion: expelled gases backwards impart forward momentum to rocket. Total momentum of rocket + exhaust gases remains conserved. No external force, so momentum conservation applies. Jet engines also work on similar principle.

Explanation:
Visible spectrum approx 400 nm (violet) to 700 nm (red).

Explanation:
The velocity of sound in a medium is determined by the formula v = √(E/ρ), where E is the modulus of elasticity and ρ is the density. Although solids are denser, their modulus of elasticity (bulk modulus) is tremendously higher than that of gases, overwhelmingly compensating for the density. Hence, sound travels fastest in solids.