Question

The correct orders among the following are:  
[A.] Atomic radius : \(B<Al<Ga<In<Tl\) 
[B.] Electronegativity : \(Al<Ga<In<Tl<B\) 
[C.] Density : \(Tl<In<Ga<Al<B\) 
[D.] 1st Ionisation Energy : 
In\(<Al<Ga<Tl<B\) 
Choose the correct answer from the options given below :

• A. B and D Only
• B. A and C Only
• C. C and D Only
• D. A and B Only

Hint:

Remember the general trends in atomic radius, electronegativity, density, and ionization energy down a group in the periodic table. Be aware of anomalies, especially in the p-block elements, due to factors like d-electron shielding and electronic configurations. For Group 13, the trends often show irregularities involving Ga and In.

Answer 1

The Correct Option is A

To identify the correct ordering of the elements B, Al, Ga, In, and Tl based on their chemical properties, an analysis of each property is presented:

1. Atomic Radius:
   Atomic radius increases down a group due to additional electron shells. The predicted order, \(B<Al<Ga<In<Tl\), is accurate.
2. Electronegativity:
   Electronegativity typically decreases down a group as the distance between the nucleus and valence electrons grows. The provided order, \(Al<Ga<In<Tl<B\), is incorrect because Boron, being the topmost element in this group, should exhibit the highest electronegativity.
3. Density:
   Density generally rises down a group for metals due to increasing atomic mass, though elemental properties can cause exceptions. The order \(Tl<In<Ga<Al<B\) contradicts expected trends and empirical data, making it incorrect.
4. 1st Ionisation Energy:
   Ionisation energy generally decreases down a group with increasing atomic size, but exceptions exist within groups. The order \(In<Al<Ga<Tl<B\) is correct, with Boron possessing the highest ionisation energy as anticipated.

Consequently, the correct sequences are identified as options B and D.