ultraviolet light.

Correct Option: D

ultraviolet light.

high refractive index.

Correct Option: B

high refractive index.

to hear a clear echo, the minimum distance should be 16.5 meter.
To hear an echo, time = 1/10 s
Velocity of sound (in air) = 330 ms ^-1
Time = 2d / Velocity of sound in air
⇒ 1/10 = 2d/330
∴ d = 16.5 metre.

Correct Option: D

to hear a clear echo, the minimum distance should be 16.5 metre.
To hear an echo, time = 1/10 s
Velocity of sound (in air) = 330 ms ^-1
Time = 2d / Velocity of sound in air
⇒ 1/10 = 2d/330
∴ d = 16.5 metre.

Sound travels fastest in metal. Increasing order of speed of sound in different mediums.
^Vgas^{< V} liquid ^{< V} solid
Sound waves cannot travel through vacuum.

Correct Option: D

Sound travels fastest in metal. Increasing order of speed of sound in different mediums.
^Vgas ^{< V} liquid ^{< V} solid
Sound waves cannot travel through vacuum.

Richter scale is used for measuring amplitude of seismic waves or intensity of earthquake.

Correct Option: C

Richter scale is used for measuring amplitude of seismic waves or intensity of earthquake.