Incorrect spelling, explanation: users of English sometimes believe that the word response is both a noun and a verb, which results in a common mistake of adding an -ed ending to it, which gives an incorrect form responsed. Indeed, it is wrong as the word response is a noun only while respond is a verb. Thus, the correct past or past participle form is responded and not responsed.

Correct spelling, explanation: the verb form responded appeared for the first time in late Middle English, but has its origin in Old French and earlier in Latin. The base form of the verb is respond and as it is a regular verb it simply takes an -ed ending in the past and past participle form, which results in the form responded.

Definition of responded
1. verb (past and past participle form) – to react to what somebody said or did,
He asked me so many questions that I got confused and responded to only a few of them.
2. verb (past and past participle form) – refers to a patient who started to get better due to the treatment,
I’m so happy that he’s responded to this experimental cancer treatment and already feels better.
3. verb (past and past participle form) – to write back,
The first day Jack came back from his holiday he responded to over a hundred emails.

Collocations with responded
The verb form responded is often followed by the words: to/that/by:
He responded to the message the moment he got it.
Kate responded that she wouldn’t make it on time.
She responded by standing up and leaving the room without saying a single word to him.