Match the following `:`
`{:(,"Column-I",,"Column-II"),((A),"Velocity",(p),"Increased,"n uarr z darr),((B), "Potential Energy",(q),"Increased,"ndarrzuarr),((C ),E_(n)-E_(n-1) (E="Total energy for H atom "(n cancel(=)1)),(r ),"Decreased,"n uarr ),((D),"Separation energy (For H atom)",(s),"No change"n uarr):}`

Answer

To solve the matching question, we will analyze each item in Column-I and determine its relationship with the items in Column-II based on the principles of atomic structure.

### Step-by-Step Solution:

1. **Velocity (A)**:
- The velocity of an electron in an atom is given by the formula \( v \propto \frac{Z}{n} \), where \( Z \) is the atomic number and \( n \) is the principal quantum number.
- As \( n \) increases, \( v \) decreases (since \( v \) is inversely proportional to \( n \)).
- Therefore, when \( n \) increases, the velocity decreases.
- This matches with option (r) "Decreased".

2. **Potential Energy (B)**:
- The potential energy of an electron in an atom is given by \( U \propto -\frac{Z}{n} \).
- As \( n \) increases, the potential energy becomes less negative (increases).
- Therefore, when \( n \) increases, the potential energy increases.
- This matches with option (p) "Increased".

3. **Energy Difference (C) \( E_n - E_{n-1} \)**:
- The energy difference between two levels in a hydrogen atom can be expressed as \( E_n - E_{n-1} \propto -\frac{Z^2}{n^2} \).
- As \( n \) increases, this energy difference decreases.
- Therefore, when \( n \) increases, \( E_n - E_{n-1} \) decreases.
- This matches with option (r) "Decreased".

4. **Separation Energy (D)**:
- The separation energy is the energy required to remove an electron from the atom and is related to the principal quantum number \( n \).
- As \( n \) increases, the separation energy also increases.
- Therefore, when \( n \) increases, the separation energy increases.
- This matches with option (q) "Increased".

### Final Matching:
- A (Velocity) → (r) "Decreased"
- B (Potential Energy) → (p) "Increased"
- C (E_n - E_{n-1}) → (r) "Decreased"
- D (Separation Energy) → (q) "Increased"

### Summary of Matches:
- A → r
- B → p
- C → r
- D → q