Questions

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.

When atoms react they do so in order to reach the lowest energy, which is the most stable. The electrons orbitals will overlap in the way that reduces the energy the most. Orbitals of similar energy will produce the greatest stabilisation.The answer you gave isn't the whole story, it depends what species is reacting with what. The effective nuclear charge on the atom will affect the energy of the valance electrons.

Hence, the reactivity of an atom arises from the existence of unpaired electrons in the valence shell.

DRDO stands for The Defence Research and Development Organisation.

The Defence Research and Development Organisation (DRDO) is an agency of the Republic of India, charged with the military's research and development, headquartered in New Delhi, India.

Subhash C. Garg, a 1983 batch lAS officer of Rajasthan cadre, has been appointed as the new the economic affairs secretary in the Union Finance Ministry. The post fell vacant after Shaktikanta Das retired on May 31, 2017. Currently, Tapan Ray, the corporate affairs secretary, has the additional charge of the economic affairs department. Prior to this appointment, Garg was Executive Director at World Bank for Bangladesh, Bhutan, India and Sri Lanka.