Which of the following expressions is a polynomial? State the reason. If an expression is a polynomial,state whether it is a polynomial in one variable or not: $x^{2}-15x+50$

(A) The given expression is $x^{2}-15x+50$.
$1$. $A$ polynomial is an algebraic expression in which the exponents of the variables are non-negative integers.
$2$. In the expression $x^{2}-15x+50$,the variable is $x$. The exponents of $x$ are $2$ and $1$,which are non-negative integers.
$3$. Therefore,it is a polynomial.
$4$. Since the expression contains only one variable $x$,it is a polynomial in one variable.