1

NEET 2021

MCQ (Single Correct Answer)
Right option for the number of tetrahedral and octahedral voids in hexagonal primitive unit cell are :
A
12, 6
B
8, 4
C
6, 12
D
2, 1

Explanation

$$\bullet$$ Number of octahedral and tetrahedral voids formed by N closed packed atoms are N and 2N respectively.

$$\bullet$$ Each hexagonal unit cell contains 6 atoms therefore, number of tetrahedral and octahedral voids are 12 and 6 respectively.
2

NEET 2021

MCQ (Single Correct Answer)
The correct option for the number of body centred unit cells in all 14 types of Bravais lattice unit cells is :
A
3
B
7
C
5
D
2

Explanation


$$\bullet$$ In 14 types of Bravais lattices, body centred unit cell is present in cubic, tetragonal and orthorhombic crystal systems.

$$\bullet$$ Hence, body centred possible variation is present in three crystal systems.
3

NEET 2020 Phase 1

MCQ (Single Correct Answer)
An element has a body centered cubic (bcc) structure with a cell edge of 288 pm. The atomic radius is :
A
$${{\sqrt 2 } \over 4} \times 288$$ pm
B
$${{4 } \over \sqrt 3} \times 288$$ pm
C
$${{4 } \over \sqrt 2} \times 288$$ pm
D
$${{\sqrt 3 } \over 4} \times 288$$ pm

Explanation

For BCC, lattice $$\sqrt 3 a = 4r$$
$$r = {{\sqrt 3 a} \over 4}$$
So, $$r = {{\sqrt 3 \times 288} \over 4}$$
4

NEET 2019

MCQ (Single Correct Answer)
A compound is formed by cation C and anion A. The anions form hexagonal close packed (hcp) lattice and the cations occupy 75% of octahedral voids. The formula of the compound is :
A
C3A4
B
C4A3
C
C2A3
D
C3A

Explanation

As anions are in hcp, the number of anions A = 6

Number of cations = 6 $$ \times $$ $${{75} \over {100}}$$

= 6 $$ \times $$ $${3 \over 4}$$ = $${9 \over 2}$$

So, formula of compound is $${C_{{9 \over 2}}}{A_6}$$.

$$ \Rightarrow $$ C9A12

$$ \Rightarrow $$ C3A4

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