Elements P, Q, R and S have atomic numbers 11, 15, 17 and 18 respectively, Which of them are reactive non-metals?

Options

A. P and Q
B. P and R
C. Q and R
D. R and S

Explanation

To determine which of the elements P, Q, R, and S are reactive non-metals based on their atomic numbers (11, 15, 17, and 18 respectively), we can follow these steps:

### Step 1: Identify the elements
- **Element P**: Atomic number 11
- **Element Q**: Atomic number 15
- **Element R**: Atomic number 17
- **Element S**: Atomic number 18

### Step 2: Determine the electronic configuration
- **Element P (Atomic number 11)**:
- Electronic configuration: 2, 8, 1
- **Element Q (Atomic number 15)**:
- Electronic configuration: 2, 8, 5
- **Element R (Atomic number 17)**:
- Electronic configuration: 2, 8, 7
- **Element S (Atomic number 18)**:
- Electronic configuration: 2, 8, 8

### Step 3: Identify the valence electrons
- **Element P**: 1 valence electron
- **Element Q**: 5 valence electrons
- **Element R**: 7 valence electrons
- **Element S**: 8 valence electrons

### Step 4: Classify the elements as metals or non-metals
- **Element P**: With 1 valence electron, it is a metal.
- **Element Q**: With 5 valence electrons, it is a non-metal.
- **Element R**: With 7 valence electrons, it is a non-metal.
- **Element S**: With 8 valence electrons, it is a noble gas (inert).

### Step 5: Determine reactivity of non-metals
- **Element Q**: Needs 3 electrons to complete its octet (reactive non-metal).
- **Element R**: Needs 1 electron to complete its octet (reactive non-metal).
- **Element S**: Has a complete octet (not reactive).

### Conclusion
The reactive non-metals among the elements P, Q, R, and S are **Q and R**.