Which of the following is the smallest unit?

Density of wood is $0.5 \; g/cm^3$ in the $CGS$ system of units. The corresponding value in $MKS$ units is?

Which of the following is not a unit of energy?

Define density and give the $MKS$ and $CGS$ units of density.

Explain this statement clearly: "To call a dimensional quantity 'large' or 'small' is meaningless without specifying a standard for comparison". In view of this,reframe the following statements wherever necessary:
$(a)$ atoms are very small objects
$(b)$ a jet plane moves with great speed
$(c)$ the mass of Jupiter is very large
$(d)$ the air inside this room contains a large number of molecules
$(e)$ a proton is much more massive than an electron
$(f)$ the speed of sound is much smaller than the speed of light.

What is the $SI$ unit of density?