When the gas to be dissolved in liquid is a/an __________ then normally co-current adsorber are used.

The correct answer is: D. Sparingly soluble gas

Explanation:
In gas absorption, the choice between co-current and counter-current flow depends on factors like solubility, heat effects, and desired efficiency.

Why co-current for sparingly soluble gases?
Sparingly soluble gases dissolve slowly in the liquid.

In co-current absorbers, both the gas and liquid enter from the same end.

This arrangement provides better temperature control and can reduce equipment corrosion or fouling, which may be critical when solubility is low and mass transfer rates are already limited.

It also helps in handling exothermic absorption reactions, which are more manageable in co-current flow due to even temperature rise.

While counter-current flow is usually more efficient, co-current is preferred when:

The gas is sparingly soluble

The process is highly exothermic

Corrosion or scaling needs to be minimized

✅ Final Answer: D. Sparingly soluble gas