Questions: When blood is acidic, hemoglobin will oxygen.

The answer is the first one: Let go of.

Explanation:

1. Let go of: When blood becomes acidic, it typically indicates an increase in carbon dioxide levels, which leads to the formation of carbonic acid and a decrease in blood pH. This condition causes hemoglobin to release oxygen more readily. This is known as the Bohr effect, where lower pH (more acidic conditions) reduces hemoglobin's affinity for oxygen, facilitating oxygen release to tissues.

2. Hold onto: This option is incorrect because, under acidic conditions, hemoglobin does not hold onto oxygen more tightly. Instead, it releases oxygen to ensure that tissues receive adequate oxygen supply despite the acidic environment.

In summary, when blood is acidic, hemoglobin will let go of oxygen.