The absorption factor refers to the efficiency of the absorption process in which a gas is dissolved into a liquid solvent. To increase the absorption factor, we need to optimize the gas flow rate (G) and solvent flow rate (S). The correct answer is option 'C', which suggests increasing 'S' and decreasing 'G'.

Explanation:

1. Gas flow rate (G):
- When the gas flow rate is increased, more gas molecules are introduced into the absorption column.
- However, if the gas flow rate is too high, the contact time between the gas and the liquid solvent decreases, reducing the absorption efficiency.
- Therefore, it is not ideal to increase 'G' to increase the absorption factor.

2. Solvent flow rate (S):
- Increasing the solvent flow rate allows for more contact between the gas and the liquid solvent, increasing the absorption efficiency.
- The solvent acts as a medium for the gas molecules to dissolve into, and by increasing the solvent flow rate, we provide more opportunities for gas molecules to come into contact with the solvent.
- Therefore, increasing 'S' can help enhance the absorption factor.

3. Optimal strategy:
- Since increasing 'G' alone is not an effective approach, and increasing 'S' alone is beneficial, the optimal strategy is to increase 'S' and decrease 'G'.
- By increasing 'S', we enhance the contact between the gas and the solvent, maximizing the absorption efficiency.
- Simultaneously, by decreasing 'G', we can maintain an appropriate contact time between the gas and the solvent, ensuring efficient absorption.
- This approach allows for a balance between gas flow rate and solvent flow rate, optimizing the absorption process and increasing the absorption factor.

In summary, to increase the absorption factor, it is recommended to increase the solvent flow rate (S) and decrease the gas flow rate (G). This strategy allows for enhanced contact between the gas and the liquid solvent, maximizing the absorption efficiency while maintaining an appropriate contact time.