Change the number (vachan) of the bracketed singular word to make it formal and grammatically respectful/collective: "(गुरु) ने प्रसन्न होकर मुझे एक मंत्र दिया।"

In Hindi, to turn certain respected singular nouns into their collective, formal plural format, suffixes like 'जन', 'वृंद', or 'गण' are added. The respectful term representing teachers/gurus collectively or formally is 'गुरुजन'. Alternatively, if it evaluates respect contextually inside this specific active phrasing where 'ने' is applied, 'गुरु' doesn't alter structurally to 'गुरुजन ने' easily unless generalized. Let's look at standard question patterns: the plural form of 'गुरु' is 'गुरुजन' or 'गुरुवृंद'. Here, 'गुरुजन' is correct.