The number of unpaired electrons in an $O_2$ molecule is

The angle between the lines $2x = 3y = -z$ and $6x = -y = -4z$ is ......... $^o$.

The number of possible enantiomeric pairs that can be produced during mono-chlorination of $2$-methylbutane is

$A$ parallel beam of monochromatic light falls normally on a single narrow slit. The angular width of the central maximum in the resulting diffraction pattern

Two particles of equal mass have velocities $\overrightarrow{v}_1=4 \hat{i} \text{ ms}^{-1}$ and $\overrightarrow{v}_2=4 \hat{j} \text{ ms}^{-1}$. The first particle has an acceleration $\overrightarrow{a}_1=(5 \hat{i}+5 \hat{j}) \text{ ms}^{-2}$ while the acceleration of the other particle is zero. The centre of mass of the two particles moves in a path of

$A$ light wave has a frequency of $4 \times 10^{14} \text{ Hz}$ and a wavelength of $5 \times 10^{-7} \text{ m}$ in a medium. The refractive index of the medium is