Consider the following orders:
(i) `HF gt HCl gt HBr gt HI`: Lewis basic character.
(ii) `CH_(4) lt C Cl_(4) lt CF_(4)`: Electornegativityy of central 'C'-atom.
(iii) `Mg^(2+) lt K^(+) lt S^(2-) lt Se^(2-)`: ionic radius
then calculate vlaue of `|x-y|^(2)`, where x and y are correct and incorrect order respectively.

Explanation

To solve the problem, we need to analyze the three given orders and determine which ones are correct and which ones are incorrect. Then, we will calculate the value of \(|x - y|^2\), where \(x\) is the number of correct orders and \(y\) is the number of incorrect orders.

### Step 1: Analyze the Lewis Basic Character Order
The order given is:
\[ HF > HCl > HBr > HI \]
To determine if this order is correct, we need to consider the Lewis basic character of these acids. The Lewis basicity is inversely related to the acidity of the corresponding acids.

- **Acidity Order**: HI > HBr > HCl > HF (because I- is the most stable conjugate base).
- **Basicity Order** (reverse of acidity): HF < HCl < HBr < HI.

Thus, the correct order for Lewis basic character is:
\[ HF < HCl < HBr < HI \]
This means the given order is incorrect.

### Step 2: Analyze the Electronegativity of Central 'C'-Atom Order
The order given is:
\[ CH_4 < CCl_4 < CF_4 \]
To determine the electronegativity of the central carbon atom in these compounds, we analyze the influence of the surrounding atoms.

- In CH4, carbon has a lower electronegativity due to hydrogen's lower electronegativity.
- In CCl4, chlorine is more electronegative than carbon, leading to a higher effective electronegativity of carbon.
- In CF4, fluorine is the most electronegative element, which pulls electron density away from carbon, increasing its effective electronegativity.

Thus, the correct order for electronegativity of the central carbon atom is:
\[ CF_4 > CCl_4 > CH_4 \]
This means the given order is incorrect.

### Step 3: Analyze the Ionic Radius Order
The order given is:
\[ Mg^{2+} < K^{+} < S^{2-} < Se^{2-} \]
To determine the correctness of this order, we analyze the ionic sizes:

- \(Mg^{2+}\) has a smaller radius due to a higher positive charge and fewer electrons.
- \(K^{+}\) is larger than \(Mg^{2+}\) because it has more electrons and is in the same period.
- \(S^{2-}\) has a larger radius than both \(Mg^{2+}\) and \(K^{+}\) because it has gained electrons, leading to increased electron-electron repulsion.
- \(Se^{2-}\) is larger than \(S^{2-}\) because it is in a lower period.

Thus, the correct order for ionic radius is:
\[ Mg^{2+} < K^{+} < S^{2-} < Se^{2-} \]
This means the given order is correct.

### Step 4: Count Correct and Incorrect Orders
- Correct orders: 1 (ionic radius)
- Incorrect orders: 2 (Lewis basic character and electronegativity)

Thus, we have:
- \(x = 1\) (correct orders)
- \(y = 2\) (incorrect orders)

### Step 5: Calculate \(|x - y|^2\)
Now we calculate:
\[ |x - y|^2 = |1 - 2|^2 = |-1|^2 = 1^2 = 1 \]

### Final Answer
The final answer is:
\[ \boxed{1} \]