1. Metal displacement: This is where a more reactive metal displaces a less reactive metal from a compound. For example:

```

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

```

Here, zinc (Zn) is more reactive than copper (Cu) and displaces it from copper sulfate (CuSO₄).

2. Hydrogen displacement: This is where a more reactive metal reacts with an acid to displace hydrogen gas. For example:

```

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

```

Here, magnesium (Mg) displaces hydrogen (H₂) from hydrochloric acid (HCl).

These are the most common types, but technically, you could also consider reactions where a halogen (like chlorine) displaces another halogen from a compound as a single-replacement reaction. However, they are less frequently mentioned in the context of single-replacement reactions.