### JEE Main Solved Paper 2017 Question 12

##### Question: A metal crystallises in a face centred cubic structure. If the edge length of its unit cell is ‘a’, the closest approach between two atoms in metallic crystal will be :- [JEE Main Solved Paper-2017]

#### Options:

A) 2a

B) $ 2\sqrt{2}a $

C) $ \sqrt{2}a $

D) $ \frac{a}{\sqrt{2}} $

## Show Answer

#### Answer:

Correct Answer: D

#### Solution:

- In FCC unit cell atoms are in contant along face diagonal So, $ \sqrt{2}a=4R $

$ \therefore $ closest distance $ (2R)=\frac{\sqrt{2}a}{2}=\frac{a}{\sqrt{2}} $