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

173.

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