Why is the $\mathrm{C}-0-\mathrm{H}$ bond angle in alcohols slightly less than the tetrahedral angle whereas the $\mathrm{C}-0-\mathrm{C}$ bond angle in ether is slightly greater?
The bond angle in 
in alcohols is slightly less than tetrahedral angle $(109^\circ 28')$. It is due to the repulsion between the unshared electron pairs of oxygen. In alcohols, two lone pair of electrons are present. Therefore, there is comparatively more repulsion and less bond angle.
The $\mathrm{C}-\mathrm{O}-\mathrm{C}$ bond angle in ether is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky $(-R)$ groups.
Explain why low molecular mass alcohols are soluble in water?
Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecule. The hydrocarbon part methoxy methane (i.e., $R$ group) tends to prevent the formation of hydrogen bonds.
Alcohols with lower molar mass will have smaller hydrocarbon part and therefore tendency to form hydrogen bonding is more and they are more soluble in water.
$$\underset{\text { (More soluble) }}{\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH}}>\underset{\text { (Less soluble) }}{\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}}$$
Explain why p-nitrophenol is more acidic than phenol?
Nitro group of phenol produces $-I$ and $-R$ effect. Because of these two effects $-\mathrm{NO}_2$ group is electron withdrawing in nature. So, the electron density in the $\mathrm{O}-\mathrm{H}$ bond of $p$-nitrophenol decreases relative to the $\mathrm{O}-\mathrm{H}$ bond of phenol.
The decrease in electron density of the $\mathrm{O}-\mathrm{H}$ bond of $p$-nitrophenol, the polarity of $\mathrm{O}-\mathrm{H}$ bond is decrease and in turn make it more acidic than phenol.
Explain why alcohols and ethers of comparable molecular mass have different boiling points?
Boiling point depends upon the strength of intermolecular forces of attraction. Higher these forces of attraction, more will be the boiling point. Alcohols undergo intermolecular hydrogen bonding. So, the molecules of alcohols are held together by strong intermolecular forces of attraction.
But in ethers no hydrogen atom is bonded to oxygen. Therefore, ethers are held together by weak dipole-dipole forces, not by strong hydrogen bond.
Since, lesser amount of energy is required than to break weak dipole-dipole forces in ethers than to break strong hydrogen bonds in alcohol.
The carbon-oxygen bond in phenol is slightly stronger than that in methanol. Why ?
Positive resonance effect is observed in phenols. Due to this $+R$ effect, lone pair of electrons of $-$OH group are in conjugation with $\pi$ electrons of the ring and the following resonance hybrid are obtained.
From the above resonating structure, it is very clear that $\mathrm{C}-\mathrm{O}$ bond of phenol acquires some partial double bond character while the $\mathrm{C}-\mathrm{O}$ bond of methanol is purely single bond. Therefore, the carbon-oxygen bond in phenol is slightly stronger than that in methanol.