21.

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room ?

• 1000 days

• 300 days

• 50 days

• 50 days

Which one of the following conformation of cyclohexane is chiral?

• Twist boat

• Rigid

• chair

• chair

Which of the following nuclear reactions will generate an isotope?

• neutron particle emission

• positron emission

• α-particle emission

• α-particle emission

The equivalent conductances of two strong electrolytes at infinite dilution in H₂O (where ions move freely through a solution) at 25°C are given below:

What additional information/quantity one needs to calculate Λ of an aqueous solution of acetic acid?

• ∧° of NaCl

• Λº of CH₃COOH

• The limiting equivalent conductance of 

• The limiting equivalent conductance of 

Which of the following species exhibits the diamagnetic behaviour?

• O₂^2–

• O₂⁺

• O₂

• O₂

The stability of dihalides of Si, Ge, Sn and Pb increases steadily in the sequence

• GeX₂ << SiX₂ << SnX₂<< PbX₂

• SiX₂ << GeX₂ << PbX₂<< SnX₂

• SiX₂ << GeX₂ << SnX₂<< PbX₂

• SiX₂ << GeX₂ << SnX₂<< PbX₂

Identify the incorrect statement among the following

• Ozone reacts with SO₂ to give SO₃

• Silicon reacts with NaOH(aq) in the presence of air to give Na₂SiO₃ and H₂O

• Cl₂ reacts with excess of NH₃ to give N₂ and HCl

• Cl₂ reacts with excess of NH₃ to give N₂ and HCl

The density (in g mL^–1) of a 3.60 M sulphuric acid solution that is 29% H₂SO₄ (Molar mass = 98 g mol^-) by mass will be 

• 1.64

• 1.88

• 1.22

• 1.22

The first and second dissociation constants of an acid H₂A are 1.0 × 10^–5 & 5.0 × 10^–10 respectively. The overall dissociation constant of the acid will be

• 5.0 × 10^–5

• 5.0 × 10¹⁵

• 5.0 × 10^–15

• 5.0 × 10^–15

A mixture of ethyl alcohol and propyl alcohol has a vapour pressure of 290 mm at 300 K. The vapour pressure of propyl alcohol is 200 mm. If the mole fraction of ethyl alcohol is 0.6, its vapour pressure (in mm) at the same temperature will be

• 350

• 300

• 360

• 360