1
MCQ (Single Correct Answer)

AIPMT 2011 Mains

A solid compound XY has NaCl structure. If the radius of the cation is 100 pm, the radius of the anion (Y$$-$$) will be
A
275.1 pm
B
322.5 pm
C
241.5 pm
D
165.7 pm

Explanation

For NaCl crystal, $${{{r_ + }} \over {{r_ - }}} = 0.414$$

Given, r+ = 100 pm

$$ \therefore $$ $${{100} \over {{r_ - }}} = 0.414$$

$$ \Rightarrow $$ $${r_ - } = {{100} \over {0.414}}$$ = 241.5 pm
2
MCQ (Single Correct Answer)

AIPMT 2010 Prelims

AB crystallizes in a body centered cubic lattice with edge length '$$a$$' equal to 387 pm. The distance between two oppositely charged ions in the lattice is
A
335 pm
B
250 pm
C
200 pm
D
300 pm

Explanation

For a bcc lattice, 2(r+ + r) = $$\sqrt 3 a$$

$$ \therefore $$ r+ + r = $${{\sqrt 3 \times 387} \over 2}$$ = 335 pm
3
MCQ (Single Correct Answer)

AIPMT 2009

Copper crystallises in a face-centred cubic lattice with a unit cell length of 361 pm. What is the radius of copper atom in pm?
A
157
B
181
C
108
D
128

Explanation

Since Cu crystallises in a face-centred cubic lattice,

Atomic radius, r = $${a \over {2\sqrt 2 }}$$

$$ \therefore $$ r = $${{361} \over {2\sqrt 2 }}$$ = 128 pm
4
MCQ (Single Correct Answer)

AIPMT 2009

Lithium metal crystallises in a body-centred cubic crystal. If the length of the side of the unit cell of lithium is 351 pm, the atomic radius of lithium will be
A
151.8 pm
B
75.5 pm
C
300.5 pm
D
240.8 pm

Explanation

Since Li crystallises in body-centred cubic

crystal, atomic radius, r = $${{\sqrt 3 a} \over 4}$$.

$$ \therefore $$ r = $${{\sqrt 3 } \over 4} \times 351$$ = 151.8 pm

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