Which of the following are Lewis acids?

Options

A. `Ag^+`
B. `[SiF_6]^(2-)`
C. `CO_2`
D. `O^(2-)`

Answer

To determine which of the following substances are Lewis acids, we need to understand the definition of a Lewis acid. A Lewis acid is a substance that can accept an electron pair.

Let's analyze the given options step by step:

1. **Option A: Silver Ion (Ag⁺)**
- Silver ion has a positive charge, which indicates that it has a tendency to accept electrons to achieve a stable electronic configuration.
- Since it can accept an electron pair, **Ag⁺ is a Lewis acid**.

2. **Option B: Silicon Hexafluoride Ion (SiF₆²⁻)**
- Silicon has an atomic number of 14, and in SiF₆²⁻, silicon is surrounded by six fluorine atoms.
- This means silicon has more than 8 electrons around it (due to the bonds with fluorine), which indicates that it has a complete octet.
- Since it does not have a tendency to accept more electrons, **SiF₆²⁻ is not a Lewis acid**.

3. **Option C: Carbon Dioxide (CO₂)**
- In CO₂, carbon is bonded to two oxygen atoms. Each bond involves sharing of electrons, and carbon has a complete octet (4 bonds).
- Since carbon's octet is complete, it does not have the tendency to accept an electron pair, making **CO₂ not a Lewis acid**.

4. **Option D: Oxide Ion (O²⁻)**
- Oxygen has an atomic number of 8, and in the oxide ion (O²⁻), it has gained two additional electrons, giving it a complete octet.
- Since it already has a full octet, it does not accept electron pairs, thus **O²⁻ is not a Lewis acid**.

After analyzing all options, we conclude that the only Lewis acid among the given options is:

**Final Answer: Option A (Silver Ion, Ag⁺)**