Which one of the following cell organelles is enclosed by a single membrane?

The major product of the following reaction is

The locus of a point $P(\alpha, \beta)$ moving under the condition that the line $y = \alpha x + \beta$ is a tangent to the hyperbola $\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$ is

When a mass $m$ is connected individually to two springs $S_1$ and $S_2$,the oscillation frequencies are $v_1$ and $v_2$. If the same mass is attached to the two springs as shown in the figure,the oscillation frequency would be

Match List-$I$ with List-$II$ and then select the correct answer from the codes given below the lists:

List-$I$	List-$II$
$A$. Butane $\to$ Isobutane	$a$. Cracking
$B$. Butane $\to$ Lower hydrocarbons	$b$. Isomerisation
$C$. $n$-Heptane $\to$ Toluene	$c$. Reed reaction
$D$. Propane $\to$ $CH_3CH_2CH_2SO_2Cl$	$d$. Aromatisation

$A$ convex lens of focal length $0.15 \ m$ is made of a material of refractive index $\frac{3}{2}$. When it is placed in a liquid,its focal length increases by $0.225 \ m$. The refractive index of the liquid is