Dipole-induced dipole interactions are present in which of the following pairs?

The correct option is HCl and He atoms.

To understand why dipole-induced dipole interactions are present between HCl and He atoms, let us break down the concepts step-by-step.

1. Understanding Dipole-Induced Dipole Interactions:
A dipole-induced dipole interaction occurs between a polar molecule (which has a permanent dipole moment) and a non-polar molecule or atom (which has no permanent dipole moment).
When the polar molecule comes close to the non-polar particle, the electrostatic field of the permanent dipole distorts the electron cloud of the non-polar particle. This distortion creates a temporary, or "induced," dipole in the non-polar species. The attraction between the permanent dipole of the first molecule and this induced dipole of the second particle is called a dipole-induced dipole interaction.

2. Analyzing the Selected Pair (HCl and He atoms):
Let's look at the nature of each species in the correct option:
- HCl (Hydrogen Chloride): Chlorine is significantly more electronegative than hydrogen. This electronegativity difference causes a shift in electron density towards the chlorine atom, resulting in a permanent dipole moment. Thus, $\mathrm{HCl}$ is a polar molecule.
- He (Helium): Helium is a noble gas existing as single atoms with a completely symmetrical sphere of electron density. It is completely non-polar and has no permanent dipole.
When a polar $\mathrm{HCl}$ molecule approaches a neutral, non-polar $\mathrm{He}$ atom, the dipole of $\mathrm{HCl}$ polarizes the electron cloud of $\mathrm{He}$, inducing a dipole on the helium atom. Consequently, a dipole-induced dipole attraction is established between them.

3. Why the other options are incorrect:
- H₂O and alcohol: Both water ($H_{2}O$) and alcohol are polar molecules capable of forming strong hydrogen bonds with each other. Their primary intermolecular forces are dipole-dipole interactions and hydrogen bonding.
- Cl₂ and CCl₄: Chlorine gas (${\mathrm{Cl}}_2$) is a homonuclear diatomic molecule, which makes it non-polar. Carbon tetrachloride (${\mathrm{CCl}}_4$) is a symmetrical tetrahedral molecule, so its individual bond dipoles cancel out, making it non-polar as well. The interaction between two non-polar species is dominated by London dispersion forces.
- SiF₄ and He atoms: Silicon tetrafluoride (${\mathrm{SiF}}_4$) is a symmetrical tetrahedral molecule where all individual bond dipoles cancel, resulting in a non-polar molecule. Since helium ($\mathrm{He}$) is also non-polar, the interaction between them is limited to dispersion forces.