Answer
(a) 3$e^{x^{2}}$ is a solution.
(b) $x e^{x^{2}}$ is not a solution.
(c) $x^{2} e^{x}$ is not a solution.
(d) $x e^{-x}$ is not a solution.
Work Step by Step
Consider the linear differential equation $y^{\prime}-2 x y=0$
(a) 3$e^{x^{2}}$ is a solution.
(b) $x e^{x^{2}}$ is not a solution.
(c) $x^{2} e^{x}$ is not a solution.
(d) $x e^{-x}$ is not a solution.