171.

Due to the presence of an unpaired electron free radicals are

• cations

• anions

• chemically inactive

• chemically reactive

Ionic radii are

• inversely proportional to effective nuclear charge

• inversely proportional to square of effective nuclear charge

• directly proportional to effective nuclear charge

• directly proportional to square of effective nuclear charge

Which one of the following arrangements represents the correct order of electron gain enthalpy (with negative sign) of the given atomic species ?

• Cl < F < S < O

• O < S < F < Cl

• S < O < Cl < F

• F < Cl < O < S

Diagonal relationship is for :

• Li - Na

• Be - Mg

• Si - Cl

• B - Si

Among NH₃, HNO₃, NaN₃ and Mg₃N₂ the number of molecules having nitrogen in negative oxidation state is

• 1

• 2

• 3

• 4

Oxygen and sulphur both are the member of same group in periodic table but H₂O is liquid while H₂S is gas because

• molecular weight of water is more

• electronegativity of sulphur is more

• H₂S  is weak acid

• water molecules are having weak hydrogen bonds between them

Diffusion of helium gas is four times faster than

• CO₂

• SO₂

• NO₂

• O₂

The pair of elements having approximately equal ionisation potential is

• Al, Ga

• Al, Si

• Al, Mg

• Al, B

Isoelectronic pair among the following is

• Ca and K

• Ar and Ca²⁺

• K and Ca²⁺

• Ar and K

On adding 1 g arsenic to 80 g benzene, the freezing' point of benzene is lowered by 0.19°C. The formula of arsenic is

• As

• As₂

• As₃

• As₄