Q. \( \text{HCl} \) is polar.

To decide whether \(\mathrm{HCN}\) (hydrogen cyanide) is polar, we need to analyze its geometry and the direction of its bond dipoles.

Step 1: Identify the molecular shape of \(\mathrm{HCN}\)

\(\mathrm{HCN}\) has three atoms total: \(\mathrm{H}\) bonded to \(\mathrm{C}\), and \(\mathrm{C}\) bonded to \(\mathrm{N}\). The valence structure shows that the carbon is bonded to two atoms (linear skeleton), and the overall molecule is linear.

So \(\mathrm{H{-}C{-}N}\) lies on a straight line, meaning the molecule has a symmetry axis through the carbon.

Step 2: Determine whether each bond is polar

Even though the molecule is linear, each bond may have a dipole because of electronegativity differences:

• \(\mathrm{H{-}C}\): carbon is more electronegative than hydrogen, so this bond has a dipole pointing toward carbon.
• \(\mathrm{C{\equiv}N}\): nitrogen is much more electronegative than carbon, so this bond has a dipole pointing toward nitrogen.

Each bond dipole points in the direction of the more electronegative atom.

Step 3: Check whether dipoles cancel or add

Because the molecule is linear, the dipoles are collinear (they lie along the same line). Whether the overall molecular dipole cancels depends on whether the bond dipoles are equal in magnitude and opposite in direction.

However, \(\mathrm{C{-}H}\) and \(\mathrm{C{\equiv}N}\) are not equivalent because \(\mathrm{H}\) and \(\mathrm{N}\) have very different electronegativities. Also, \(\mathrm{C{-}H}\) is a single bond, while \(\mathrm{C{\equiv}N}\) is a triple bond, so the electron distribution is very different.

Therefore, the dipole from the \(\mathrm{C{\equiv}N}\) bond is stronger than the dipole from the \(\mathrm{C{-}H}\) bond.

Step 4: Conclude polarity

Since the dipoles do not cancel completely, \(\mathrm{HCN}\) has a net dipole moment.

Final Answer: \(\mathrm{HCN}\) is polar.