What is the Boyle temperature?

Given van der Waals constant $a$ for $NH_{3}$,$H_{2}$,$O_{2}$ and $CO_{2}$ are respectively $4.17$,$0.244$,$1.36$ and $3.59$,which one of the following gases is most easily liquefied?

$A$ gas behaves as an ideal gas under which of the following conditions?

What is the compressibility factor $(Z)$ for the deviation of real gases from ideal behavior?

What is the value of $Z$ for an ideal gas and a real gas?

Which of the following represents the Van der Waals equation for $n$ moles of a gas?