The air around us; the clouds above. although we cannot see them, both the air and the clouds are made up of these building blocks of matter called a) atoms. b) compounds. c) electrons. d) protons.

Option (A) is the correct answer.

Explanation:

An atom is defined as the smallest unit of a matter because when a number of atoms combine together then it leads to the formation of matter.

For example, solid, liquid and gaseous are all states of matter.

A compound is defined as a chemical specie which is made by the combination of different atoms in a fixed ratio by mass.  

For Example, , etc. are compounds.

Electrons are one of the sub-atomic particles which are present outside the nucleus of an atom and revolve around it.

Protons are another sub-atomic particles which are present inside the nucleus of an atom.

Thus, we can conclude that the air around us; the clouds above. Although we cannot see them, both the air and the clouds are made up of these building blocks of matter called atoms.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.