Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

11.

Metals are good conductor of electricity because they contain :

  • a network structure

  • ionic bonds

  • very few valence electrons

  • free electrons


D.

free electrons

Metals are good conductor of electricity because they contain free electrons .


12.

The elements commonly used for making transistors are :

  • Ga and In

  • C and Si

  • P and As

  • Si and Ge


B.

C and Si

D.

Si and Ge

Si and Ge are used for making transistors .


13.

What is binding energy in B511 nucleus , if mass is 0.08181 amu ?

  • 1.2 x 10-4 erg/nucleus

  • 8.2 x 10-4 erg/nucleus

  • 10.2 x 10-4 erg/nucleus

  • 1.9 x 10-4 erg/nucleus


A.

1.2 x 10-4 erg/nucleus

1 amu = 1.66 x 10-24 g

E = mc2

c = velocity of light (3 x 1010 cm/s)

= 1.66 X 10-24 g X (3 x 1010 cm/s)2

= 1.49 x 10-3 ergs

Binding energy = mass defect x E

= 1.2 x 10-4 erg/nucleus

Note : It is per nucleus and not per nucleon


14.

Which of the compound is optically active ?

  • 1 - butanol

  • Ethanol

  • 2 - butanol

  • Isopropyl alcohol


D.

Isopropyl alcohol

A compound could be optically active only when it contains at least one asymmetric carbon atom or chiral centre .


15.

Which is the strongest acid ?

  • ClCH2COOH

  • CH3COOH

  • Cl2CHCOOH

  • CCl3COOH


D.

CCl3COOH

CCl3COOH is the strongest acid because (-I) nductive effect increases with increase in number of chlorine atoms and therefore , acidic strength also increases .


16.

Hydrofluoric acid shows hydrogen bonding due to :

  • high electron affinity of fluorine

  • high bond dissociation energy of fluorine

  • high electronegativity of fluorine

  • none of the above


C.

high electronegativity of fluorine

Hydrofluoric acid shows the intermolecular hydrogen bonding due to the small size of fluorine and high electronegativity of fluorine .

Note :  Hydrofluoric acid is found in polymeric compound [(HF)n] and liquid state due to then H-bonding .


17.

Crystalline form of silica is called :

  • crystalline silicon

  • quartz

  • rock

  • talc


B.

quartz

Crystalline form of silica is called quartz .


18.

Among third row elements , the IP value :

  • irregularly changes from left to right across the third row

  • increases from left to right across the third row

  • decrease for Na to Ar

  • remains constant


B.

increases from left to right across the third row

In the third row's elements , the value of ionisation potential increases from left to right with breaks , where the atoms have some what stable configuration .

Third row's element Na Mg Al Si P S Cl Ar
IP (eV) 5.1 7.6 6.0 8.0 11.0 10.4 13.0 15.8


19.

The conjugate base of (CH3)2NH2+ is :

  • (CH3)3N

  • (CH3)2NH

  • (CH3)2N-

  • (CH3)2N+


B.

(CH3)2NH

An acid is a substance which has a tendency to donate H+ ion and gives conjugated base .(Bronsted concept)

(CH3)2NH2+acid-H+  (CH3)2NHconjugate base


20.

A buffer solution contains 500 mL of 0.2 M CH3COONa and 500 ml of 0.1 M CH3COOH .1 L of water is added to this buffer , pH before and after dilution will be (pka of CH3COOH = 4.74)

  • 3.74

  • 5.04

  • 5.90

  • 7.70


B.

5.04

CH3COONa  CH3COO- + Na+

pH of buffer = pKa + log [CH3COO-][CH3COOH]

= 4·74 + log 500 × 0.2500 × 0.1

= 5.04

pH of a buffer does not change with dilution .