Question

Which of the following is the correct increasing order of atomic number of elements A, B and C of third period, if their oxides are amphoteric, basic and acidic in nature respectively?

• A. B < A < C
• B. A < B < C
• C. C < A < B
• D. B < C < A

Hint:

Left to right in a period: Basic $\rightarrow$ Amphoteric $\rightarrow$ Acidic.

Answer 1

The Correct Option is A

Step 1: Recall the oxide trend across a period.
As we move left to right across a period, the metallic nature drops and the elements become more non-metallic. Because of this, the nature of their oxides changes from basic, to amphoteric, to acidic.

Step 2: Match the words to real third-period oxides.
In period 3: sodium gives $Na_2O$ which is basic, aluminium gives $Al_2O_3$ which is amphoteric, and phosphorus gives $P_4O_{10}$ which is acidic.

Step 3: Assign the labels.
The question says A is amphoteric, B is basic, and C is acidic. So A is aluminium, B is sodium, and C is phosphorus.

Step 4: Put their atomic numbers in order.
Sodium $Z=11$, aluminium $Z=13$, phosphorus $Z=15$. So B $(11)$ < A $(13)$ < C $(15)$.

Step 5: Conclusion.
The increasing order of atomic number is $B < A < C$. \[ \boxed{B < A < C} \]