What does the part labeled as "$X$" represent in the given figure?

Which of the following substances leads to the inhibition of the central nervous system?

Which one of the following molecules contains both ionic and covalent bonds?

Anxiety and eating spicy food together in an otherwise normal human may lead to:

$A$ clock pendulum made of invar has a period of $0.5 \, s$ at $20^{\circ} C$. If the clock is used in a climate where the temperature averages to $30^{\circ} C$, how much time does the clock lose in each oscillation? (For invar, $\alpha = 9 \times 10^{-7} /{ }^{\circ} C$, $g = \text{constant}$)

$\lim _{x \rightarrow 0} \left( \frac{x \cdot 10^x - x}{1 - \cos x} \right)$ is equal to