Select the correct statement.

Which of the following factors favour the dissociation of $HbO_2$ at the tissue level?

When acetaldehyde is heated with Fehling solution,a red precipitate is formed. Which of the following is that?

When a liquid is heated in a copper vessel, its coefficient of apparent expansion is $6 \times 10^{-6} /{ }^{\circ} C$. When the same liquid is heated in a steel vessel, its coefficient of apparent expansion is $24 \times 10^{-6} /{ }^{\circ} C$. If the coefficient of linear expansion for copper is $18 \times 10^{-6} /{ }^{\circ} C$, what is the coefficient of linear expansion for steel?

The angle between the lines represented by $y^2 \sin^2 \theta - xy \sin^2 \theta + x^2(\cos^2 \theta - 1) = 0$ is

If $u = x y^2 \tan^{-1}\left(\frac{y}{x}\right)$, then $x \frac{\partial u}{\partial x} + y \frac{\partial u}{\partial y}$ is equal to