Questions

In purifying drinking water alum is used for coagulation of mud particles.

Central Processing Unit (CPU) is the brain of any computer system.

6:45

Explanation: As you move from left to right, add 1 to the value of each digit on the watch, and rotate the digits one place to the left.

Because the refractive index of glass is highest, light travels slowly in Glass. 

We know that the speed of light depends on the refraction index. The higher the index of refraction is, the slower the speed of light is.

R.I of air and vacuum = 0 (air is a teeny bit more but can be taken as 0)
R.I of water = 1.33
R.I of glass = 1.4.

Hence, Light travels slowest in Glass.