Three centred bond is present in

Options

A. `NH_3`
B. `B_2 H_6`
C. `BCl_3`
D. `AlCl_3`

Explanation

To solve the question regarding the presence of three-centered bonds, we will analyze the molecular structures of several compounds and identify where three-centered bonds occur.

### Step-by-Step Solution:

1. **Understanding Three-Centered Bonds**:
- A three-centered bond involves three atoms sharing two electrons. This type of bond is often found in certain boron compounds.

2. **Analyzing Different Compounds**:
- **NiS3**: This compound has a structure with three covalent bonds, but they are all two-centered bonds. Thus, it does not contain a three-centered bond.
- **BCl3**: This molecule has a trigonal planar structure with all two-centered bonds. Therefore, it also does not contain a three-centered bond.
- **AlCl3**: In its monomeric state, AlCl3 contains ionic bonds and does not exhibit three-centered bonding.
- **B2H6 (Diborane)**: This is the key compound we are interested in. It contains two boron atoms and forms a structure where two of the bonds are three-centered bonds.

3. **Identifying the Three-Centered Bonds in B2H6**:
- In diborane, the structure includes two terminal B-H bonds and two B-H-B bonds. The B-H-B bonds are the three-centered bonds.
- Each B-H-B bond involves two electrons shared between three atoms (two boron atoms and one hydrogen atom). This is specifically referred to as a "banana bond" or a "3-centered 2-electron bond".

4. **Conclusion**:
- The three-centered bonds are present in B2H6 (diborane). Therefore, the answer to the question is B2H6.

### Final Answer:
Three-centered bonds are present in **B2H6 (Diborane)**.