After three days of taking a selective serotonin reuptake inhibitor (SSRI), Derrek is disappointed because he is not feeling any better. However, it generally takes for this type of antidepressant to reach full effect.

Weeks.

Explanation:

Selective serotonin reuptake inhibitors are common antidepressants prescribed for patients with depression and anxiety disorders. However, these medications do not have an immediate effect. They usually have full effect within weeks, depending on the patient.

This delay, can be explained by the mechanism of action of these drugs. Selective serotonin reuptake inhibitors act by blocking the serotonin transporter which transports serotonin into the brain cells.This results in more being available outside the cells where it has it effects.

SSRIs don't work instantaneously because they do not target the transporter directly. They rather, bind to the DNAs that produce the transporter and therefore makes them less active and this leads to lower amount of transporters available. This process takes time.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds