What are scalar numbers?
Just real numbers, which can have any value (so they can be fractions as well as whole numbers).
The opposite of a scalar quantity is a vector quantity, which has direction as well as magnitude.
In the context of balancing equations, we can have whole numbers in front of the formulae of the reactants and products, so that the same number of each atom occurs on each side of the equation:
Or we can use fractions, so long as the equation is still balanced.
Both are correct, and there are some times when we want to use fractions,me.g. Defining enthalpy changes of combustion or formation.