Which of the following is not an antibiotic?

In a $\triangle ABC$,if $\frac{a}{b^2-c^2} + \frac{c}{b^2-a^2} = 0$,then $B$ is equal to

The figure shows three resistor configurations $R_1, R_2$,and $R_3$ connected to a $3\,V$ battery. If the power dissipated by the configurations $R_1, R_2$,and $R_3$ is $P_1, P_2$,and $P_3$ respectively,then:

The potential energy of a particle of mass $m$ is given by,$U(x) = \begin{cases} E_0 & 0 \leqslant x \leqslant 1 \\ 0 & x > 1 \end{cases}$. $\lambda_1$ and $\lambda_2$ are the de-Broglie wavelengths of the particle when $0 \leqslant x \leqslant 1$ and $x > 1$ respectively. If the total energy of the particle is $2 E_0$,the ratio $\frac{\lambda_1}{\lambda_2}$ will be

Which of the following has provided the main food source for humans?

The $P-V$ diagram of $2$ g of helium gas for a certain process $A \to B$ is shown in the figure. What is the heat given to the gas during the process $A \to B$ (in ${P_0}{V_0}$)?