Questions

The puzzle's logic is

1st figure : (9-7) + (8-5) = 2 + 3 = 5

2nd figure : (15-6) + (11-2) = 9 + 9 = 18

similarly, 3rd figure : (9-6) + (17-5) = 3 + 12 = 15.

The given compund Li3PO4 name is Lithium phosphate.

Lithium phosphate is a white crystal at room temperature. It is slightly soluble in water.

It  can be used to produce glass, disk, colorful phosphor powder. It can also be used as a catalyst in some reactions.

As there is no medium inside the bell jar, sound cannot travel

A standing wave also known as a stationary wave, is a wave in which its peaks or any other point on the wave do not move spatially.

This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. The most common cause of standing waves is the phenomenon of resonance, in which standing waves occur inside a resonator due to interference between waves reflected back and forth at the resonator's resonant frequency.

Hence, standing wave occurs when a wave reflects upon itself.