1

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

In general, the properties that decrease and increase down a group in the periodic table, respectively, are :
A
B
Electron Gain Enthalpy and Electronegativity.
C
D
Electronegativity and Electron Gain Enthalpy.

## Explanation

Electronegativity decreases down the group because the increased number of energy levels puts the outer electrons very far away from the pull of nucleus.

Atomic radius increases down the group because the number of energy levels increases when you move down the group. Each subsequent energy level is further from the molecules than the last. That is why atomic radius increases down the group.
2

### 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
3

### 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)
4

### 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