Which of the following electronic configurations is not possible according to Hund's rule?

The potential energy for a force field $\vec{F}$ is given by $U(x, y) = \cos(x + y)$. The force acting on a particle at the position given by coordinates $(0, \pi/4)$ is:

The $pH$ of water is $7$. When a substance $Y$ is dissolved in water,the $pH$ becomes $13$. The substance $Y$ is a salt of

The $pH$ of $0.05 \ M$ acetic acid is $(K_a = 2 \times 10^{-5})$

Which of the following groups is not an auxochrome?

When a current of $2\,A$ flows in a battery from negative to positive terminal,the potential difference across it is $12\,V$. If a current of $3\,A$ flows in the opposite direction,the potential difference across the terminals of the battery is $15\,V$. The emf of the battery is ............... $V$.