Is 5x a numerical expression or a algebraic expression?

5x is an algebraic expression because it contains a constant (5) and a variable (x)

It's an algebraic expression. "x" is a variable and 5 is a constant.
 
An algebraic expression is a phrase used in math that contains numbers and variables. ( Such as x, or y) It also has operators. ( Multiply, Divide, Add, Subtract.)
 
A numerical expression is a sentence in math that uses only numbers and operation symbols.
 
   Hope this helps!
         ~ 231agoad