"在从事社交活动的" 可以翻译为 "while engaging in social activities" 或者 "when participating in social activities"。例如：
He tends to be more outgoing while engaging in social activities. （他在从事社交活动时往往更外向。）
She feels more confident when participating in social activities. （她在参加社交活动时感觉更自信。）