Answer:
One kind of atom.
Step-by-step explanation:
An <em>element</em> consists of one kind of atom.
Al is an element, so Al consists of one kind of atom.
C and D are <em>wrong</em> , because Al contains only atoms of aluminium.
Because Mg stands before H on the metal reactivity scale
Hope this helps!! And maybe makes you smile!! I struggle with chemistry as well (and I’m in AP chem ;) )