Which is most reactive elements among Na, mg and al?​

Explanation:

As we move from left to right in a period the chemical reactivity of a metal decreases and of non-metal increases. Hence Na is most reactive as it is the first element of period 3.

sodium(Na)

Explanation:

A reactive metal has the ability to easily lose an electron and acquire a positive charge. Sodium easily loses electrons and acquires a positive charge. Sodium easily lose electrons than magnesium and get oxidized to easily.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !