Which of the following is the most stable conformer of butane?

In Young's double slit experiment,the phase difference between the light waves reaching the third bright fringe from the central fringe is $(\lambda = 6000 \ \mathring{A})$

$A$ fully charged capacitor $C$ with initial charge $q_0$ is connected to a coil of self-inductance $L$ at $t=0$. The time at which the energy is stored equally between the electric and the magnetic field is

The total work done on a particle is equal to the change in its kinetic energy. This is applicable:

$A$ gamma ray photon creates an electron-positron pair. If the rest mass energy of an electron is $0.5 \, MeV$ and the total $K.E.$ of the electron-positron pair is $0.78 \, MeV$,then the energy of the gamma ray photon must be .......... $MeV$.

If the circle $x^2+y^2+8x-4y+c=0$ touches the circle $x^2+y^2+2x+4y-11=0$ externally and cuts the circle $x^2+y^2-6x+8y+k=0$ orthogonally,then $k=$