The very first atmosphere of earth was composed mostly of hydrogen atoms and these atoms due to light weight were very active. Thus,it was a reducing atmosphere during primitive time.

The correct answer is option 'B': Hydrogen atoms were active and in greater number.

Explanation:
The primitive atmosphere of Earth is believed to have primarily consisted of gases such as methane (CH4), ammonia (NH3), water vapor (H2O), and hydrogen (H2). However, over time, the composition of the atmosphere changed due to various processes, including the escape of gases into space and the activity of living organisms.

1. Composition of the primitive atmosphere:
- Hydrogen (H2) was abundant in the primitive atmosphere.
- Methane (CH4), ammonia (NH3), and water vapor (H2O) were also present in significant amounts.
- Oxygen (O2) was scarce, and nitrogen (N2) was not present in the primitive atmosphere.

2. Escape of gases into space:
- Hydrogen (H2) being the lightest element had a propensity to escape into space due to its low molecular weight.
- Over time, a significant amount of hydrogen was lost from the atmosphere, resulting in a decrease in its concentration.
- This loss of hydrogen contributed to the reduction of the primitive atmosphere.

3. Chemical reactions and formation of compounds:
- Hydrogen (H2) is a highly reactive gas and readily participates in chemical reactions.
- The active hydrogen atoms reacted with other gases present in the atmosphere, such as oxygen (O2) and nitrogen (N2).
- As a result, these reactive hydrogen atoms formed compounds like water (H2O) and ammonia (NH3).
- The formation of these compounds reduced the concentration of hydrogen in the atmosphere.

4. Role of living organisms:
- Over time, the evolution of living organisms, particularly photosynthetic bacteria and plants, led to the significant alteration of the atmosphere.
- These organisms released oxygen (O2) as a byproduct of photosynthesis, increasing its concentration in the atmosphere.
- The increased availability of oxygen allowed for the formation of ozone (O3) in the upper atmosphere, which helped protect life on Earth from harmful ultraviolet radiation.

In summary, the primitive atmosphere was reducing because hydrogen atoms were active and in greater number. The escape of hydrogen into space, chemical reactions leading to the formation of compounds, and the influence of living organisms played a role in reducing the concentration of hydrogen in the atmosphere over time.