The correct order of gases evolved on fractional distillation of liquid air is provided in option 2: H2, Ne, N2, O2.

To understand why this order is correct, we need to consider the boiling points of these gases. The process of fractional distillation separates a mixture of liquids or gases based on their boiling points. The components with lower boiling points will vaporize and rise to the top first, while those with higher boiling points will remain as liquids or sink to the bottom.

Firstly, H2 (hydrogen) has the lowest boiling point among these gases, so it will be the first to evaporate and be collected.

Next, Ne (neon) has a slightly higher boiling point compared to hydrogen, so it will be collected next after hydrogen.

Then, N2 (nitrogen) has a higher boiling point than hydrogen and neon, so it will be collected after hydrogen and neon.

Lastly, O2 (oxygen) has the highest boiling point among these gases, so it will be collected last.

In conclusion, the correct order of gases evolved on fractional distillation of liquid air is H2, Ne, N2, O2, as stated in option 2.