Question

which comparison is correct? (1 point) o h₂s is a stronger acid than hcl. o ph₃ is a stronger acid than nh₃. o nh₃ is a stronger acid than hf. o hf is a stronger acid than hcl.

Explanation:

Step1: Recall acid - strength trends

Acid - strength depends on factors like bond strength and electronegativity. In the halogen - hydride series (HX), as we move down the group, the H - X bond strength decreases and acid strength increases. So, $HCl$ is a stronger acid than $HF$. Also, among hydrides of group 15 elements, the basicity decreases down the group, which means the conjugate acid strength of their conjugate bases increases.

Step2: Analyze each option

• For $H_2S$ and $HCl$: Chlorine is more electronegative than sulfur and the $H - Cl$ bond is more polar and weaker than the $H - S$ bond. So, $HCl$ is a stronger acid than $H_2S$.
• For $PH_3$ and $NH_3$: Nitrogen is more electronegative than phosphorus. $NH_3$ is a stronger base than $PH_3$, so the conjugate acid of $PH_3$ (i.e., $PH_4^+$) is a stronger acid than the conjugate acid of $NH_3$ (i.e., $NH_4^+$), or $PH_3$ is a stronger acid than $NH_3$ in terms of the acid - base behavior of their conjugate species.
• For $NH_3$ and $HF$: $HF$ is a weak acid but is more acidic than $NH_3$ because fluorine is highly electronegative and the $H - F$ bond can dissociate to a greater extent compared to the $N - H$ bond in $NH_3$.
• For $HF$ and $HCl$: As mentioned above, $HCl$ is a stronger acid than $HF$ due to the weaker $H - Cl$ bond compared to the $H - F$ bond.

Answer:

$PH_3$ is a stronger acid than $NH_3$.