Which of the following acts as both an oxidizing agent and a reducing agent?

Anhydrous $Na_2CO_3$ is also known as

$A$ point object is placed at the centre of a glass sphere of radius $6 \, cm$ and refractive index $1.5$. The distance of the virtual image from the surface of the sphere is.....$cm$.

If $\frac{dy}{dx} = \frac{y + x \tan(\frac{y}{x})}{x}$,then $\sin(\frac{y}{x})$ is equal to

$Br_2 + 2X^{-} \to 2Br^{-} + X_2$
$Cl_2 + 2Y^{-} \to 2Cl^{-} + Y_2$
The incorrect match regarding the above reactions is:

Which of the following has the lowest melting point?