Practice problems on JEE Mains, JEE Mains 2005

Question 1

t1/4​ can be taken as the time taken for the concentration of a reactant to drop to 3/4 of its initial value. If the rate constant for a first order reaction is k, the t1/4​ can be written as

Accepted Answer

0.29/k

Answer

0.75/k

Answer

0.69/k

Answer

0.10/k

Question 2

Consider an endothermic reaction X→Y with the activation energies Eb​ and Ef​ for the backward and forward reactions respectively. In general

Accepted Answer

Eb​<Ef​

Answer

there is no definite relation between Eb​ and Ef​

Answer

Eb​=Ef​

Answer

Eb​>Ef​

Question 3

A schematic plot of lnKeq​ versus inverse of temperature for a reaction is shown below  The reaction must be

Accepted Answer

exothermic

Answer

highly spontaneous at ordinary temperature

Answer

one with negligible enthalpy change

Answer

endothermic

Question 4

The structure of diborane (B2​H6​) contains

Accepted Answer

four 2c−2e−bonds and two 3c−2e−bonds

Answer

four 2c−2e−bonds and four 3c−2e−bonds

Answer

two 2c−2e−bonds and two 3c−3e−bonds

Answer

two 2c−2e−bonds and four 3c−2e−bonds

Question 5

The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is

Accepted Answer

two

Answer

three

Answer

one

Answer

zero

Question 6

In silicon dioxide

Accepted Answer

each silicon atom is surrounded by four oxygen atoms and each oxygen atom is bonded to two silicon atoms

Answer

there are double bonds between silicon and oxygen atoms

Answer

silicon atom is bonded to two oxygen atoms

Answer

each silicon atom is surrounded by two oxygen atoms and each oxygen atom is bonded to two silicon atoms

Question 7

The value of the 'spin only' magnetic moment for one of the following configurations is 2.84BM. The correct one is

Accepted Answer

d4 (in strong ligand field)

Answer

d5 (in strong ligand field)

Answer

d3 (in weak as well as in strong fields)

Answer

d4 (in weak ligand field)

Question 8

Which of the following compounds shows optical isomerism?

Accepted Answer

[Cr(C2​O4​)3​]3−

Answer

[Co(CN)6​]3−

Answer

[ZnCl4​]2−

Answer

[Cu(NH3​)4​]2+

Question 9

Which one of the following species is diamagnetic in nature?

Accepted Answer

H2​

Answer

H2−​

Answer

H2+​

Answer

He2+​

Question 10

The best reagent to convert pent-3-en-2-ol into pent-3-en-2-one is

Accepted Answer

chromic anhydride in glacial acetic acid

Answer

pyridinium chloro-chromate

Answer

acidic dichromate

Answer

acidic permanganate

Question 11

Lattice energy of an ionic compound depends upon

Accepted Answer

charge on the ion and size of the ion

Answer

packing of ions only

Answer

size of the ion only

Answer

charge on the ion only

Question 12

The molecular shapes of SF4​,CF4​ and XeF4​ are

Accepted Answer

different with 1,0 and 2 lone pair of electrons on the central atom, respectively

Answer

different with 0,1 and 2 lone pair of electrons on the central atom, respectively

Answer

the same with 1,1 and 1 lone pair of electrons on the central atom, respectively

Answer

the same with 2,0 and 1 lone pair of electrons on the central atom, respectively