Which one of the following metallic hydroxides does not dissolve in sodium hydroxide solution?

An inductor and a resistor are connected in series to an $AC$ source of $10 \ V$. If the potential difference across the inductor is $6 \ V$,then the potential difference across the resistor is: (in $V$)

Which of the following oxides will not react with $NaOH$?

$A$ parallel beam of light is incident on a system of two convex lenses of focal lengths $f_1 = 20\, cm$ and $f_2 = 10\, cm$. What should be the distance between the two lenses so that the rays after refraction from both the lenses emerge as a parallel beam?........$cm$

Let $\vec{p}$ and $\vec{q}$ be the position vectors of points $P$ and $Q$ with respect to the origin $O$,and $|\vec{p}| = p$,$|\vec{q}| = q$. If points $R$ and $S$ divide the line segment $PQ$ internally and externally in the ratio $2:3$ respectively,and if $\vec{OR} \perp \vec{OS}$,then:

Which is the best material for studying mitosis in a laboratory?