To find the most common molecule in living things, let's carefully consider each of the given options:
A. [tex]\( \text{H}_2\text{O} \)[/tex]
- Water is a vital component of all living organisms. It plays essential roles in chemical processes, temperature regulation, and acts as a solvent for many biochemical reactions.
B. [tex]\( \text{CO} \)[/tex] (Carbon monoxide)
- Carbon monoxide is not a common molecule in living things. In fact, it is a poisonous gas that can be deadly in high concentrations. It binds with hemoglobin in the blood, preventing oxygen transport.
C. [tex]\( \text{CO}_2 \)[/tex] (Carbon dioxide)
- Carbon dioxide is involved in processes such as respiration and photosynthesis. However, it is not as abundantly present in living organisms as water.
D. [tex]\( \text{H}_2 \)[/tex] (Hydrogen gas)
- Molecular hydrogen is not commonly found in significant amounts in living organisms. It is not involved in many of the critical biological processes necessary for life.
From the analysis above, option A ([tex]\( \text{H}_2\text{O} \)[/tex]) is the most common molecule in living things due to its vital role in various biological functions and its abundance in organisms.
Therefore, the most common molecule in living things is water ([tex]\( \text{H}_2\text{O} \)[/tex]).
So, the correct answer is:
1. [tex]\( \text{H}_2\text{O} \)[/tex]
