Read the passage given below and answer the following questions:
In transition elements, generally, ions of the same charge in a given series show progressive decrease in radius with increasing atomic number. This is because the new electron enters a d orbital each time the nuclear charge increases by unity. But the radii of the third (5d) series are virtually the same as those of the corresponding members of the second series. This phenomenon is associated with the intervention of the 4f orbitals which must be filled before the 5d series of elements begin. The filling of 4f before 5d orbital results in a regular decrease in atomic radii called Lanthanoid contraction.
Following are the transition metal ions of 3d series:
`Ti^(4+), v^(2+), Mn^(3+), Cr^(3+)`
(Atomic number: Ti = 22, V = 23, Mn = 25, Cr = 24)
Assertion (A): `Ti^(4+)` ion is colourless.
Reason (R): All valence electrons are unpaired in `Ti^(4+)` ion.

Options

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statement but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement

Explanation

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided in the context of the titanium (Ti) ion.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the `Ti^(4+)` ion is colorless.
- To determine if this is true, we need to look at the electronic configuration of the `Ti^(4+)` ion.

2. **Finding the Electronic Configuration of Titanium**:
- The atomic number of Titanium (Ti) is 22. Its ground state electronic configuration is:
\[ \text{Ti: } [\text{Ar}] 3d^2 4s^2 \]
- When titanium loses 4 electrons to form `Ti^(4+)`, it loses the 2 electrons from the 4s orbital and 2 electrons from the 3d orbital:
\[ \text{Ti}^{4+}: [\text{Ar}] 3d^0 \]
- This means that the `Ti^(4+)` ion has no electrons in the d-orbitals.

3. **Color and Electronic Transitions**:
- The color of transition metal ions is typically due to the presence of unpaired electrons in the d-orbitals. These unpaired electrons can absorb light to promote themselves to higher energy levels, resulting in color.
- Since `Ti^(4+)` has a d-electron configuration of `3d^0`, it has no unpaired electrons.

4. **Conclusion on Assertion (A)**:
- Since `Ti^(4+)` has no unpaired electrons, it cannot absorb light in the visible spectrum and is therefore colorless.
- Thus, the assertion (A) is **true**.

5. **Understanding the Reason (R)**:
- The reason states that "All valence electrons are unpaired in `Ti^(4+)` ion."
- We have already established that `Ti^(4+)` has a `3d^0` configuration, which means there are no d-electrons at all.

6. **Conclusion on Reason (R)**:
- Since there are no valence electrons in the d-orbitals (as they are all removed), the statement that "all valence electrons are unpaired" is **false**.

7. **Final Evaluation**:
- Assertion (A) is true, while Reason (R) is false. Therefore, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion (A) is true.
- Reason (R) is false.