Chapter 1 - Equations and Inequalities - 1.1 Linear Equations - 1.1 Exercises - Page 92: 10

Option $(B)$

A linear equation is an equation whose variable's greatest degree is $1$. The equations in $A$, $C$, and $D$ have variables whose greatest degree is $1$ so all of them are linear equations. The equation in $B$ involves a variable whose greatest degree is $2$. Thus, the equation is not linear.