Lagrange's Theorem: In any finite group G, the order (number of elements) of every subgroup of G divides the order of G.
Here G is the group with an order $12$.So it’s factor are: $1,2,3,4,6,12$
$\therefore 1,2,3,4,6,12$ six subgroups are there.
Lagrange's Theorem-based question: