Coal tar is the main source of

$\begin{aligned} & f(x, y)=2(x-y)^2-x^4-y^4 \\ & \left|\left(f_{x x} f_{y y}-f_{x y}^2\right)\right|_{(0,0)} \end{aligned}$

Five very long,straight wires are bound together to form a small cable. Currents carried by the wires are $I_1 = 20\ A, I_2 = -6\ A, I_3 = 12\ A, I_4 = -7\ A, I_5 = 18\ A$. The magnetic induction at a distance of $10\ cm$ from the cable is

$A$ 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 .......... $MeV$.

Anhydrous $Na_2CO_3$ is also known as

Bordeaux mixture was discovered by