The correct option is A x+4=0
An linear equation in one variable is an equation which has only one variable, and the highest power of that variable is "one". Here, only (x+4=0) is a linear equation in one variable.
(x3+3=0) is an equation whose highest power of the variable is three. Hence, it is not a linear equation.
(x+2) and (xy+5) are algebraic expressions. They are not equations.