In a regular trigonal bipyramidal `MX_(5)`, the number of X - M - X bonds at `180^(@)` is

Options

A. One
B. two
C. six
D. Four

Answer

To determine the number of X - M - X bonds at 180° in a regular trigonal bipyramidal molecule \( MX_5 \), we can follow these steps:

### Step 1: Understand the Geometry of \( MX_5 \)
In a trigonal bipyramidal geometry, there are five substituents (X atoms) around a central atom (M). The arrangement consists of two distinct types of positions: three atoms in a plane (equatorial position) and two atoms above and below this plane (axial position).

**Hint:** Visualize the structure of the trigonal bipyramidal shape to understand the positions of the atoms.

### Step 2: Identify the Bond Angles
In this geometry:
- The equatorial X atoms are separated by 120° from each other.
- The axial X atoms are aligned directly opposite each other, resulting in a bond angle of 180°.

**Hint:** Remember that axial positions are directly opposite each other, which leads to the 180° bond angle.

### Step 3: Count the 180° Bonds
In the \( MX_5 \) structure:
- There are two axial positions, and thus there is one bond angle formed between the two axial X atoms through the central M atom.
- Therefore, there is only **one** X - M - X bond that is at 180°.

**Hint:** Focus on the axial positions when considering bonds at 180°.

### Step 4: Conclusion
Thus, in a regular trigonal bipyramidal \( MX_5 \), the number of X - M - X bonds at 180° is **1**.

**Final Answer:** 1