The number of atoms in $100 \text{ g}$ of an $fcc$ crystal with density $d = 10 \text{ g/cm}^3$ and cell edge equal to $100 \text{ pm}$ is equal to:

When a large bubble rises from the bottom of a lake to the surface, its radius doubles. If atmospheric pressure is equal to that of a column of water of height $H$, then the depth of the lake is:

Assertion $(A)$: The $pH$ of a buffer solution containing equal moles of acetic acid and sodium acetate is $4.8$ ($pK_a$ of acetic acid is $4.8$).
Reason $(R)$: The ionic product of water at $25^{\circ} C$ is $10^{-14} \ mol^2 \cdot L^{-2}$. The correct answer is

Water-containing cavities in vascular bundles are found in:

$300 \text{ g}$ of water at $25^{\circ} \text{C}$ is added to $100 \text{ g}$ of ice at $0^{\circ} \text{C}$. The final temperature of the mixture will be (in $^{\circ} \text{C}$)

The basis of the quantum mechanical model of an atom is