The answer is non-native, harmful.
Answer: 1m/s
Explanation: according to the law of conservation of linear momentum in an isolated system, the momentum of the gun equals that of the bullet.
Mathematically
Mb×Vb = Mg×Vg
Where Mb = mass of bullet = 1/100 = 0.01 kg
Vb = velocity of bullet = 200 m/s
Mg = mass of gun = 2kg
Vg = recoil velocity of gun =?
0.01×200 = 2×Vg
Vg = 0.01×200/2
Vg = 0.01×100
Vg = 1m/s

Actually Welcome to the Concept of the Wave Optics.
Whenever the waves are out of phase they form a DESTRUCTIVE interference.
thus,
Destructive Interference occurs when two waves are out of phase.
It is correct! good job :)