The binding of oxygen to fe^{2+} in the first heme pushes the iron ion out of the porphyrin ring, decreasing the affinity for the second oxygen.
true / false.

False

Explanation:

The uptake and the release of the oxygen in the hemoglobin is monitored by a effect known as cooperative effect. It states hat when one oxygen molecules i being added to one of the four heme units of  the hemoglobin, there will be some structural changes in the heme which further facilitates the uptake of the oxygen for the second heme and thus further facilities for the other two heme units with much greater rates.

This is same with the release of oxygen from one unit of the hemoglobin which further facilitates the removal of the oxygen from other units. Hence, the given statement is false.