For a given principal level n = 5, the energy of its subshells is of the order:

Options

A. s lt d lt f lt p
B. s lt p lt d lt f
C. d lt f lt p lt s
D. s lt p lt f lt d

Explanation

To determine the energy order of subshells for a given principal level \( n = 5 \), we will use the \( n + l \) rule. Here’s a step-by-step solution:

### Step 1: Identify the Principal Quantum Number
The principal quantum number \( n \) is given as 5. This indicates we are looking at the fifth energy level.

### Step 2: Identify the Azimuthal Quantum Numbers
The azimuthal quantum number \( l \) defines the subshells:
- For \( s \) subshell, \( l = 0 \)
- For \( p \) subshell, \( l = 1 \)
- For \( d \) subshell, \( l = 2 \)
- For \( f \) subshell, \( l = 3 \)

### Step 3: Calculate \( n + l \) for Each Subshell
Now, we will calculate \( n + l \) for each subshell at \( n = 5 \):
- For \( 5s \): \( n + l = 5 + 0 = 5 \)
- For \( 5p \): \( n + l = 5 + 1 = 6 \)
- For \( 5d \): \( n + l = 5 + 2 = 7 \)
- For \( 5f \): \( n + l = 5 + 3 = 8 \)

### Step 4: Determine the Order of Energy
According to the \( n + l \) rule, the lower the \( n + l \) value, the lower the energy of the subshell. Therefore, we can arrange the subshells in order of increasing energy:
- \( 5s \) (5)
- \( 5p \) (6)
- \( 5d \) (7)
- \( 5f \) (8)

### Final Order of Energy
Thus, the order of energy for the subshells at \( n = 5 \) is:
\[ 5s < 5p < 5d < 5f \]

### Conclusion
The energy of its subshells is of the order \( s < p < d < f \).

---