Which of the following molecules possesses polar bonds but is non-polar?

A molecule has polar bonds if there is a difference in electronegativity between the bonded atoms. A molecule is non-polar if its overall dipole moment is zero, meaning the individual bond dipoles cancel out due to molecular symmetry.

*   Sulphur(IV) oxide ($SO_2$) has polar S-O bonds and a bent shape, making it a polar molecule.
*   Carbon(IV) oxide ($CO_2$) has polar C-O bonds. However, its linear geometry means the two equal and opposite bond dipoles cancel each other out, resulting in a non-polar molecule.
*   Ammonia ($NH_3$) has polar N-H bonds and a trigonal pyramidal shape, making it a polar molecule.
*   Water ($H_2O$) has polar O-H bonds and a bent shape, making it a polar molecule.

Therefore, the molecule with polar bonds but a non-polar overall structure is $\boxed{\text{Carbon(IV) oxide}}$.

An alkyl group is a functional group derived from an alkane by removing one hydrogen atom.

The general formula for an alkane is $C_nH_{2n+2}$.

By removing one hydrogen atom from an alkane, the general formula for an alkyl group becomes $C_nH_{2n+1}$.

The general formula of an alkyl group is $\boxed{C_nH_{2n+1}}$.

The equation is $MgCl_2 + 2H_2O \rightarrow Mg(OH)_2 + 2HCl$. In this reaction, a salt ($MgCl_2$) reacts with water ($H_2O$) to produce a base ($Mg(OH)_2$) and an acid ($HCl$).

*   **Hydrolysis** is a chemical reaction in which water reacts with a substance to break it down into two or more new substances.
*   **Hydration** is the process of adding water molecules to a substance, often forming a hydrate, without necessarily breaking the original compound.
*   **Neutralization** is the reaction between an acid and a base to form a salt and water.
*   **Ionization** is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, or by the dissociation of a molecule into ions.

The reaction of $MgCl_2$ with water to form $Mg(OH)_2$ and $HCl$ is a classic example of a salt undergoing hydrolysis.

The reaction represented by the equation is $\boxed{\text{hydrolysis}}$.