Question

Hydrogen burns in air with a
A. Light bluish flame
B. Yellow flame
C. Green flame
D. None of these

Answer 1

Hint: All elements are made up of electrons, protons & neutrons. Protons and neutrons are closely bound to each other in the nucleus of atoms. But electrons can freely revolve around the nucleus and they can leave an atom if a sufficient amount of energy is applied to the atoms. Now if the elements are burned they give a characteristic colour to the flame because each element has a specific number of free electrons based on that they give colour to the flame.

Complete Step by Step Answer:
Each atom has a specific no. of free electrons; when some energy (in the form of heat) is applied to these or they are burnt in the presence of flame the electrons get excited and jump to a higher energy state but don’t stay in the excited energy state they leave their energy in the form of photons ( light particles) and comes back to their ground state. This process results in the colour of the flame.

The colour of the flame depends on the energy released in the form of photons. And this energy of the emitted photons is based on the difference between the energy gap of the energy levels. So the colours of flames are distinctive and characteristic for each element.
The colour of flames of some elements are-
Sodium - Persistent Orange
Potassium - Lilac (pink)
Calcium - Orange-Red
Copper - Blue-Green
Lead - Grey-White
Thus; experimentally the colour of the flame of pure hydrogen fuel is pale blue flame or light bluish flame.
Thus, Option (A) is correct

Note: You can see a yellow flame while burning hydrogen because of the presence of impurities. Not all elements give their characteristic colours to the flame.