Answer:
Tamoxifen is an irreversible, competitive inhibitor.
Step-by-step explanation:
In order to binds to the active site of the estrogen receptor protein, tamoxifen have to compete with the other chemical compound, and inhibits the estrogen release, so it is a competitive inhibitor. Then, you said that when tamoxifen binds to the receptor, the protein is permanently deactivated, so it is also irreversible.