Which one has the maximum oxidation number of phosphorus?

Select the correct pair from the following.

The time taken for a calorimeter containing $75 \ g$ of water at $62^{\circ} C$ to cool to $58^{\circ} C$ is $9 \ \text{minutes}$. When the calorimeter contains $105 \ g$ of water, it takes $12 \ \text{minutes}$ to cool from $62^{\circ} C$ to $58^{\circ} C$. The water equivalent of the calorimeter is: (in $g$)

Which of the following statements are correct for alkali metal compounds?
$(i)$ Superoxides are paramagnetic in nature.
$(ii)$ The basic strengths of hydroxides increase down the group.
$(iii)$ The conductivity of chlorides in their aqueous solutions decreases down the group.
$(iv)$ The basic nature of carbonates in aqueous solutions is due to cationic hydrolysis.

If $\lambda_0$ is the de-Broglie wavelength for a proton accelerated through a potential difference of $100 \ V$,the de-Broglie wavelength for an $\alpha$-particle accelerated through the same potential difference is

Which structure acts as the pacemaker of the heart?