Which of the following accurately describes properties of valence?
a. the smaller the number of electrons an atom has to borrow or to lend, the greater the activity of the atom.
b. metals tend to have a negative valence and tend to be electron borrowers.
c. the greater the number of electrons an atom has to borrow or to lend, the greater the activity of the atom.
d. nonmetallic elements tend to have a positive valence and tend to be electron borrowers.

Option (A) is the correct answer.

Explanation:

Valence electrons are defined as the electrons present in the outermost shell of an atom.

Smaller is need for valence electrons to be borrowed or to lend more is the reactivity of an atom.

For example, atomic number of fluorine is 9 and its electronic distribution is 2, 7.

So, it just needs one more electron in order to gain stability. Therefore, it will be highly reactive in nature.

Thus, we can conclude that the smaller the number of electrons an atom has to borrow or to lend, the greater the activity of the atom, accurately describes properties of valence.

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.