5. a charged object is able to repel a) only charged objects
b) neutral objects and neutral particles
c) neutral objects but not neutral particles
d) only neutral particles

A) only charged objects

Explanation:

The electrostatic force between two objects is given by

where

k is the Coulomb's constant

q1, q2 are the charges of the two objects

r is the separation between the two objects

We have:

- If the charges have same sign (q1 and q2 have same sign), the force is repulsive

- if the charges have opposite sign (q1 and q2 have opposite sign), the force is attractive

If one of the object is neutral, its charge is zero: q=0, so the electrostatic force is also zero.

So, the correct option is

A) only charged objects

because all the other options (B, C and D) involve the presence of neutral particles, for which q=0 and so the electrostatic force is also zero.

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.