S-block element having formula of oxide `MO_2`, which is yellow and paramagnetic is

Options

A. Na
B. K
C. Ca
D. Mg

Answer

To solve the problem of identifying the S-block element with the oxide formula \( MO_2 \) that is yellow and paramagnetic, we can follow these steps:

### Step 1: Identify the S-block elements
S-block elements include Group 1 (alkali metals) and Group 2 (alkaline earth metals) of the periodic table. The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkaline earth metals are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

**Hint:** Remember that S-block elements are characterized by having their outermost electrons in the s orbital.

### Step 2: Analyze the oxide formula \( MO_2 \)
The oxide formula \( MO_2 \) indicates that the metal (M) is in a +4 oxidation state. This is atypical for most S-block elements, as they usually form oxides in lower oxidation states. However, we can consider the possibility of peroxides or superoxides.

**Hint:** Consider the oxidation states of the S-block elements when they react with oxygen.

### Step 3: Check the known oxides of S-block elements
- **Sodium (Na)** forms \( Na_2O \) and \( Na_2O_2 \) (peroxide).
- **Potassium (K)** forms \( K_2O \) and \( KO_2 \) (superoxide).
- **Calcium (Ca)** forms \( CaO \).

Among these, potassium is known to form \( KO_2 \), which can be represented as \( K^+ + O_2^- \). The \( O_2^- \) ion is a superoxide.

**Hint:** Look for the specific oxides that correspond to the formula \( MO_2 \).

### Step 4: Determine the color and magnetic properties
The oxide \( KO_2 \) is known to be yellow in color. Additionally, the \( O_2^- \) ion contains unpaired electrons, making it paramagnetic.

**Hint:** Recall that paramagnetic substances have unpaired electrons, which can be confirmed through molecular orbital theory.

### Step 5: Conclusion
The S-block element with the oxide formula \( MO_2 \) that is yellow and paramagnetic is potassium (K).

**Final Answer:** The element is potassium (K).