The correct option is option (d) $x+\frac{3}{x}$ is not a polynomial.
It is because in the second term, the degree of $x$ is $-1$ and an expression with a negative degree is not a polynomial.
Which of the following is not a polynomial? (a) $\sqrt{3} x^{2}-2 \sqrt{3} x+5$ (b) $9 x^{2}-4 x+\sqrt{2}$ (c) $\frac{3}{2} x^{3}+6 x^{2}-\frac{1}{\sqrt{2}} x-8$ (d) $x+\frac{3}{x}$
Which of the following is not a polynomial? (a) $\sqrt{3} x^{2}-2 \sqrt{3} x+5$ (b) $9 x^{2}-4 x+\sqrt{2}$ (c) $\frac{3}{2} x^{3}+6 x^{2}-\frac{1}{\sqrt{2}} x-8$ (d) $x+\frac{3}{x}$