1
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

A metal crystallises with a face-centred cubic lattice. The edge of the unit cell is 408 pm. The diameter of the metal atom is
A
288 pm
B
408 pm
C
144 pm
D
204 pm

Explanation

Given $$a$$ = 408 pm

For the face centred cubic structure

r = $${a \over {2\sqrt 2 }}$$ = $${{408} \over {2\sqrt 2 }}$$ = 144 pm

$$ \therefore $$ Diameter = 2r = 2$$ \times $$144 = 288 pm
2
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
3
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
4
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

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