Which of the following has the highest critical temperature?

h2
n2
nh3
h2o

The answer is:  H2O

The critical temperature (also known as the critical point) is the temperature above a vapor or gas can't be liquefied no matter how many pressure can be applied. Every substance has a critical temperature which varies according to the substance/compound nature.

For example, the water has a critical temperature of  373.94 °C, it means that above that temperature the vapor and liquid phases can't be distinct and there is no possible way that the vapor became liquid again no matter how many pressure is applied.

The critical temperature of the given elements/compounds are:

H2 : -240 °C

N2: -147 °C

NH3: 132.4 °C

H2O: 373.94 °C

Have a nice day!

"the periodic table is arranged in order of atomic number."

it is stable as it is in group 0 which have full outer shells of electrons