In an atom,the order of increasing energy of electrons with quantum numbers $(i)$ $n=4, l=1$,$(ii)$ $n=4, l=0$,$(iii)$ $n=3, l=2$,and $(iv)$ $n=3, l=1$ is:

Which of the following taxonomic categories is being described by the given statements $(i-iii)$?
$(i)$ It is the basic unit of classification.
$(ii)$ It is defined as the group of individuals which resemble in their morphological and reproductive characters and interbreed among themselves and produce fertile offsprings.
$(iii)$ Human beings belong to the species sapiens which is grouped in the genus Homo.

Ferric sulphate on heating gives:

The work functions for metals $A, B$ and $C$ are respectively $1.92\, eV$,$2.0\, eV$ and $5\, eV$. According to Einstein's photoelectric equation,the metals which will emit photoelectrons for a radiation of wavelength $4100\, \mathring{A}$ is/are:

Animals devoid of respiratory,excretory,and circulatory organs are:

The angle between the lines whose direction cosines satisfy the equations $l+m+n=0$ and $l^2+m^2-n^2=0$ is