Question

is the set of whole numbers a group under divison

Answer 1

If \(G\) is a group, and \(a \in G\) and \(b \in G\), then a group requires \(a * b \in G\) (as one of the requirements). If \(*\) is division, then take \(a=3, b=2\)... \(3\div 2 =1.5 \notin G\)

Answer 2

just that indicates it wouldn't be a group