Which of the following is not an antibiotic?

Two dice are thrown simultaneously,the probability of obtaining a total score of $5$ is

The tension $T$ in the string shown in the figure is:

The derivative of ${\tan ^{ - 1}}\left( {\frac{{\sqrt {1 + {x^2}} - 1}}{x}} \right)$ with respect to ${\tan ^{ - 1}}\left( {\frac{{2x\sqrt {1 - {x^2}} }}{{1 - 2{x^2}}}} \right)$ at $x = 0$ is:

Blood must pass through the ........ to reach the left side of the heart.

$A$ cell of $emf$ $E$ and internal resistance $r$ is connected in series with an external resistance $nr$. Then,the ratio of the terminal potential difference to $emf$ is