NEET-XII-Chemistry
Previous Year Paper year:2018
- #59Iron exhibits bcc structure at room temperature.
Above 900°C, it transforms to fcc structure. The
ratio of density of iron at room temperature to that
at 900°C (assuming molar mass and atomic radii of
iron remains constant with temperature) is
(1)``\frac{\sqrt3}{\sqrt2}``
(2)``\frac{4\sqrt3}{3\sqrt2}``
(3)``\frac{3\sqrt3}{4\sqrt2}``
(4)``\frac{1}{2}``digAnsr: 3Ans : (3)
Sol. BCC FCC
4r = 3a 4r = 2a
a =
4r
3
a =
4r
2
BCC
FCC
d
d =
BCC
3
A
FCC
3
A
Z M
N a
Z M
N a
=
3
A
3
A
2 M
4r
N
3
4 M
4r
N
2
=
3 3
4 2