What is the correct order of the following layers in the atmosphere with height? Select the correct answer from the codes given below :
(a) Atomic Hydrogen Layer
(b) Atomic Oxygen Layer
(c) Helium Layer
(d) Nitrogen Layer
Codes :

Question

What is the correct order of the following layers in the atmosphere with height? Select the correct answer from the codes given below :
(a) Atomic Hydrogen Layer 
(b) Atomic Oxygen Layer 
(c) Helium Layer 
(d) Nitrogen Layer
Codes :

Accepted Answer

Here's a detailed explanation justifying why Option 4 (d, b, c and a) is the correct order of the atmospheric layers with increasing height, and why the other options are incorrect:

**Why Option 4 (d, b, c and a) is Correct:**

Option 4 suggests the order: Nitrogen Layer, Atomic Oxygen Layer, Helium Layer, Atomic Hydrogen Layer. This order aligns with the principles of atmospheric composition and density stratification.

*   **Nitrogen Layer (d):** Nitrogen is a relatively heavier element compared to oxygen, helium, and hydrogen. In the lower thermosphere and exosphere, molecular nitrogen (N2) is still present, though it starts to dissociate into atomic nitrogen at higher altitudes. However, it's generally found at lower altitudes than the other atomic layers listed.

*   **Atomic Oxygen Layer (b):** As altitude increases, solar radiation becomes more intense. This radiation causes the dissociation of molecular oxygen (O2) into atomic oxygen (O). Atomic oxygen is lighter than molecular nitrogen and thus resides at a higher altitude. The peak concentration of atomic oxygen is found in the thermosphere.

*   **Helium Layer (c):** Helium is a very light noble gas. Due to its low atomic mass, it rises above the heavier atomic oxygen layer. Helium becomes a dominant constituent in the upper thermosphere and lower exosphere.

*   **Atomic Hydrogen Layer (a):** Hydrogen is the lightest element. Consequently, atomic hydrogen (H) resides at the highest altitudes in the exosphere. It's the most abundant element at the outer fringes of the atmosphere, gradually transitioning into the vacuum of space.

Therefore, the density stratification of the atmosphere, with heavier elements/molecules at lower altitudes and lighter elements at higher altitudes, supports the order: Nitrogen, Atomic Oxygen, Helium, Atomic Hydrogen.

**Why Other Options are Incorrect:**

*   **Option 1 (a, b, c and d):** This option suggests the order: Atomic Hydrogen, Atomic Oxygen, Helium, Nitrogen. This is incorrect because it places the lightest element (Hydrogen) at the lowest altitude and the heavier element (Nitrogen) at the highest, which contradicts the principles of atmospheric density stratification.

*   **Option 2 (d, c, b and a):** This option suggests the order: Nitrogen, Helium, Atomic Oxygen, Atomic Hydrogen. While it correctly places Nitrogen at a lower altitude than Helium, it incorrectly places Helium below Atomic Oxygen. Helium is lighter than atomic oxygen and should be above it.

*   **Option 3 (a, c, b and d):** This option suggests the order: Atomic Hydrogen, Helium, Atomic Oxygen, Nitrogen. This is incorrect because it places the lightest element (Hydrogen) at the lowest altitude and the heavier element (Nitrogen) at the highest, which contradicts the principles of atmospheric density stratification. It also incorrectly places Helium below Atomic Oxygen.