1

### JEE Main 2019 (Online) 9th January Evening Slot

When the first electron gain enthalpy $\left( {{\Delta _{eg}}H} \right)$ of oxygen is $-$ 141 kJ/mol, its second electron gain enthalpy is :
A
a more negative value than the first
B
almost the same as that of the first
C
negative, but less negative than the first
D
a positive value

## Explanation

Second electron gain enthalpy is always positive for every element.
O$-$(g) + e$-$ $\to$ O$-$2(g) ; $\Delta$H = positive
2

### JEE Main 2019 (Online) 10th January Morning Slot

The electronegativity of aluminium is similar to :
A
Beryllium
B
Carbon
C
Boron
D
Lithium

## Explanation

E.N. of Al = (1.5) $\cong$ Be (1.5)
3

### JEE Main 2019 (Online) 10th January Morning Slot

The effect of lanthanoid contraction in the lanthanoid series of elements by and large means :
A
B
increase in both atomic and ionic radii
C
decrease in both atomic and ionic radii
D

## Explanation

4

### JEE Main 2019 (Online) 10th January Evening Slot

The 71st electron of an element X with an atomic number of 71 enters into the orbital;
A
4f
B
6s
C
6p
D
5d

## Explanation

In lutetium (71Lu) the 71st electron enters in 5d-orbital.

Electron configuration is [Xe]4f145d16s2