Which one of the following happenings in the classroom is an activity?

The correct option is Children engaged in exploration.

Understanding Activity-Based Learning in the Classroom:

An educational activity involves active, hands-on participation where learners engage directly with their environment, construct knowledge, experiment, and think critically, rather than passively receiving information.

Analysis of Options:

1. Teacher explaining how to do sums: This represents a direct instruction method where the teacher is active, but the students are primarily listening passive recipients.

2. Children reciting counting in form of rhymes: While rhythmic, rote repetition or singing rhymes often involves passive memory rehearsal rather than active exploration or dynamic learning activities.

3. Children copying from blackboard: Copying text or math solutions is a passive, mechanical task that requires minimal active cognitive engagement or creative involvement.

4. Children engaged in exploration: Exploration involves active engagement, curiosity, problem-solving, and hands-on discovery by students, which perfectly defines an authentic classroom activity.

Therefore, Children engaged in exploration is the correct choice.