21.

Which of the following carbocations will be most stable ?

• ${\mathrm{Ph}}_3{\mathrm{C}}^{+}$

• ${\mathrm{CH}}_3-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$

• $({\mathrm{CH}}_3{)}_2\stackrel{+}{\mathrm{C}}\mathrm{H}$

• ${\mathrm{CH}}_2=\mathrm{CH}-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$

A compound is formed by substitution of two chlorine for two hydrogens in propane. The number of possible isomeric compounds is

• 4

• 3

• 2

• 5

Which one of the following formulae does not represent an organic compound ?

• C₄H₁₀O₄

• C₄H₆O₄

• C₄H₇ClO₄

• C₄H₉O₄

If n_t number of radio atoms are present at time t, the following expression will be a constant

• $\frac{{\mathrm{n}}_{\mathrm{t}}}{\mathrm{t}}$

• $\ln \frac{{\mathrm{n}}_{\mathrm{t}}}{\mathrm{t}}$

• $\frac{\mathrm{d}}{\mathrm{dt}}(\ln \mathrm{nt})$

• $\mathrm{t}·{\mathrm{n}}_{\mathrm{t}}$

The following graph shows how t_1/2 (half-life) of a reactant, R changes with the initial reactant concentration a_0. The order of the reaction will be

• 0

• 1

• 2

• 3

The time taken for 10% completion of a first order reaction is 20 min. Then, for 19% completion, the reaction will take

• 40 min

• 60 min

• 30 min

• 50 min

The half-life of a radioactive element is 10 h. How much will be left after 4 h in 1 g atom sample?

• 45.6 x 10²³ atom

• 4.56 x 10²³ atom

• 4.56 x 10²¹ atom

• 4.56 10²⁰ atom

In Cu-ammonia complex, the state of hybridisation of Cu²⁺ is

• sp³

• d³s

• sp²f

• dsp²

Of the following acids the one which has the capability to form complex compound and also possesses oxidising and reducing properties is

• HNO₃

• HNO₂

• HCOOH

• HCN

Atoms in a P₄ molecule of white phosphorus are arranged regularly in the following way

• at the corners of a cube

• at the corners of an octahedron

• at the corners of a tetrahedron

• at the centre and corners of a tetrahedron