Answer:
V = 6.55*10^{-6} v
Explanation:
The number density can be determined by using below formula:

where,
B is uniform magnetic field 0.74
i is current 18 A
V is hall potential difference
l is thickness 150 MICRO METER
e is electron charge 1.6 *10^{-19} C
therefore V can be determined as


V = 6.55*10^{-6} v
C) is the correct answer.
Answer
given,
wavelength (λ) = 650 nm
angle = 5°
using bragg's law



d = 7.46 x 10⁻⁴ cm
number of slits per centimeter
= 
b) wavelength of two rays 650 nm and 420 nm

d = 2 x 10⁻6 m
we now,

for 650 nm


θ = 40.54°
for 450 nm


θ = 24.83°
now, difference
|θ_{650} -θ_{420}| =40.54°-24.83°
|θ_{650} -θ_{420}| =19.71°