responding
v.v. to say or write something as an answer to a question or a message. It also means to react to something that happens.
v. the present participle of 'respond', meaning to reply in words or to react to a stimulus. Transitive when followed by a 'that' clause; otherwise typically intransitive.
She is responding to your email right now.
The emergency services are responding to a call about a fire in the city center.
While the patient is responding well to the new medication, doctors remain cautious about the long-term effects on his immune system.
Typically intransitive and requires the preposition 'to' before the object.
He is responding the questionHe is responding to the questionRespond is intransitive and requires the preposition 'to' before a noun or pronoun object.