The electronic configuration of an element is `1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(3)`. What is the atomic number of the element which is just below the above element in the periodic table ?
49
31
34
33

Options

A. 49
B. 31
C. 34
D. 33

Answer

To find the atomic number of the element that is just below the given element in the periodic table, we can follow these steps:

### Step 1: Determine the Atomic Number of the Given Element
The electronic configuration provided is:
\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^3 \]

To find the atomic number, we need to count the total number of electrons in this configuration. The atomic number is equal to the total number of electrons.

- \( 1s^2 \): 2 electrons
- \( 2s^2 \): 2 electrons
- \( 2p^6 \): 6 electrons
- \( 3s^2 \): 2 electrons
- \( 3p^3 \): 3 electrons

Now, we add these together:
\[ 2 + 2 + 6 + 2 + 3 = 15 \]

Thus, the atomic number of the element is **15**.

### Step 2: Identify the Element Below in the Periodic Table
The element with atomic number 15 is phosphorus (P), which has the configuration ending in \( 3p^3 \). The element just below phosphorus will have its last electrons in the \( 4p \) subshell.

The electronic configuration of the element just below phosphorus will be:
\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^{10} \, 4p^3 \]

### Step 3: Calculate the Atomic Number of the Element Below
To find the atomic number of the element below phosphorus, we can count the electrons in the new configuration:
- \( 1s^2 \): 2 electrons
- \( 2s^2 \): 2 electrons
- \( 2p^6 \): 6 electrons
- \( 3s^2 \): 2 electrons
- \( 3p^6 \): 6 electrons (fully filled)
- \( 4s^2 \): 2 electrons
- \( 3d^{10} \): 10 electrons
- \( 4p^3 \): 3 electrons

Now, we add these together:
\[ 2 + 2 + 6 + 2 + 6 + 2 + 10 + 3 = 33 \]

Thus, the atomic number of the element just below phosphorus is **33**.

### Conclusion
The atomic number of the element which is just below the element with the electronic configuration \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^3 \) is **33**.