From which part of the plant is cocoa obtained from $Theobroma$ $cacao$?

Two radioactive materials $X_1$ and $X_2$ have decay constants $10 \lambda$ and $\lambda$ respectively. If initially they have the same number of nuclei,then the ratio of the number of nuclei of $X_1$ to that of $X_2$ will be $1 / e$ after a time:

$A$ ball is let fall from a height $h_0$. It makes $n$ collisions with the earth. After $n$ collisions it rebounds with a velocity $v_n$ and the ball rises to a height $h_n$. Then the coefficient of restitution is given by:

$A$ molecule $M$ associates in a given solvent according to the equation $nM \rightleftharpoons (M)_n$. For a certain concentration of $M$,the van't Hoff factor was found to be $0.9$ and the fraction of associated molecules was $0.2$. The value of $n$ is:

The molecular formula of compound $A$ is $C_2Cl_3OH$. It reduces Fehling's solution and on oxidation gives a monocarboxylic acid $B$. Compound $A$ is obtained by the reaction of chlorine with ethyl alcohol. What is $A$?

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k$ is equal to :