Among the following , the number of elements showing only one non-zero oxidation state is:
`O,C,F,N,P,Sn,Tl,Na,Ti`

Explanation

To determine the number of elements from the given list that show only one non-zero oxidation state, we will analyze each element individually.

### Step-by-Step Solution:

1. **Identify the Elements**: The elements provided are O (Oxygen), C (Carbon), F (Fluorine), N (Nitrogen), P (Phosphorus), Sn (Tin), Tl (Thallium), Na (Sodium), Ti (Titanium).

2. **Analyze Each Element for Oxidation States**:
- **Oxygen (O)**:
- Common oxidation states: -2 (most common), -1 (in peroxides), +2 (in OF2), and +4 (in compounds like O2Cl2).
- **Conclusion**: More than one oxidation state.

- **Carbon (C)**:
- Common oxidation states: -4, +2, +4.
- **Conclusion**: More than one oxidation state.

- **Fluorine (F)**:
- Common oxidation state: -1 (it is the most electronegative element and does not show any positive oxidation state).
- **Conclusion**: Only one oxidation state (-1).

- **Nitrogen (N)**:
- Common oxidation states: -3, +1, +2, +3, +4, +5.
- **Conclusion**: More than one oxidation state.

- **Phosphorus (P)**:
- Common oxidation states: -3, +3, +5.
- **Conclusion**: More than one oxidation state.

- **Tin (Sn)**:
- Common oxidation states: +2, +4.
- **Conclusion**: More than one oxidation state.

- **Thallium (Tl)**:
- Common oxidation states: +1, +3.
- **Conclusion**: More than one oxidation state.

- **Sodium (Na)**:
- Common oxidation state: +1 (as an alkali metal, it shows only this state).
- **Conclusion**: Only one oxidation state (+1).

- **Titanium (Ti)**:
- Common oxidation states: +2, +3, +4.
- **Conclusion**: More than one oxidation state.

3. **Count the Elements with Only One Non-Zero Oxidation State**:
- From the analysis, the elements showing only one non-zero oxidation state are:
- Fluorine (F) with -1
- Sodium (Na) with +1

4. **Final Count**:
- Total number of elements showing only one non-zero oxidation state = 2 (Fluorine and Sodium).

### Answer:
The number of elements showing only one non-zero oxidation state is **2**.

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