Question

Light travels fastest in
A) Air
B) Water
C) Glass
D) Diamond

Answer 1

A) air
$3 \times {10}^{8} m {s}^{ - 2}$

Answer 2

A) Air is your answer. Actually it travels fastest in vacuum, but the option isn’t mentioned so air. It’s speed in air is almost 3 x 10^8 m/sec whereas in vacuum it is exactly 3 x 10^8 m/sec.