Which of the following alkaline earth metal nitrides is volatile?

Which one among the following is likely to have the highest levels of $DDT$ depositions in its body?

Three rods of the same dimensions have thermal conductivities $3 K, 2 K$,and $K$. They are arranged as shown in the figure below. The temperature of the junction in the steady state is:

In a series of $2n$ observations,half of them are equal to $a$ and the remaining half are equal to $-a$. If the standard deviation of the observations is $2$,then $|a|$ is equal to:

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

How many species are there in the genus $Homo$?