Light year is a unit of 

Persons suffering from myopia are advised to use

X-rays are _________ waves.

It is possible to store pollen grains of a large number of species for year’s in-

How many bones are found in children? 

Once the mass of a solid is doubled, its density is-

The pH of acid rain is

A yellow dust appears on the fingers, whenever we touch the middle of a flower. These tiny yellow grains are one of the most precious substances in nature because they contain the secret of plant life.  What is this dust called?