Question

Check whether the sets $A$ and $B$ are disjoint:
$A$ is the set of all hydrogen atoms in this universe, $B$ is the set of all water molecules on earth

Answer 1

$A=$ The set of all hydrogen atom in this universe.

$B=$ The set of all water molecules on Earth.

$A$ and $B$ are not disjoint becaude water molecules contain hydrogen atoms

water Molecules $H_{2}O$.