The order of first ionization energies of the elements Li, Be, B, Na is :

• Li> Be> B > Na

• Be > B > Li > Na

• Na > Li > B> Be

• Be > Li > B > Na

The standard adopted for the determination of atomic weight of elements is based on :

• H¹

• C¹²

• O¹⁶

• S³²

In the periodic table metallic character of elements shows one of the following trend :

• decreases down the group and increases across the period

• increases down the group and decreases across the period 

• increases across the period and also down the group

• decreases across the period and also down the group

Radioactive decay series of Uranium is denoted as:

• 4n + 1

• 4n + 2

• 4n

• 4n + 3

Number of unpaired electrons in sulphur is

• 2

• 6

• 8

• 1

Oxygen molecule contains :

• no unpaired electron

• one unpaired electron

• two unpaired electrons

• three unpaired electrons

77.

Among 3^rd row elements atomic size is maximum for

• sodium

• argon

• magnesium

• chlorine

Number of electrons in the valence orbit of nitrogen in an ammonia molecule is

• 8

• 5

• 6

• 7

The product obtained on fusion of BaSO₄ and Na₂CO₃ is

• BaCO₃

• BaO

• Ba(OH)₂

• BaHSO₄

The electronic configuration of elements A, B and C are [He] 2s¹, [Ne] 3s¹ and [Ar] 4s¹ respectively, which one of the following order is correct for the first ionization potentials (in kJ mol^-1) of A , B and C?

• A > B > C

• C > B > A

• B > C > A

• C > A > B