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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Chemistry
Chapter
Solid State

NTA Abhyas 2020 · Chemistry · Solid State

The density of KBr is 2.75gcm^ - 3 , length of the unit cell is 654...

The density of KBr is 2.75gcm−32.75gcm^{- 3} , length of the unit cell is 654 pm. K = 39, Br = 80, then what can be true about the predicted nature of the solid?
(Given: NA=6.023×1023{N}_{A} = 6.023 \times {10}^{23})

Options

  1. ASolid has face centred cubic system with co-ordination number = 6
  2. BSolid has simple cubic system with co-ordination number = 8
  3. CSolid has face centred cubic system with co-ordination number =12
  4. DNone of the above

Correct answer

A. Solid has face centred cubic system with co-ordination number = 6

Step-by-step solution

Given that& ρ=2.75gcm−3\text{ρ} = 2.75\text{g}\text{c}m^{- 3}

we need to find type of unit cell&

& ∴ρ=Z×MNAa3∵Z=ρ×NA×a3M=2.75×6.023×1023×(654×10−10)3119\begin{array}{ll}∴ \text{ρ} = \dfrac{\text{Z} \times \text{M}}{{N}_{A} a^{3}} \\ ∵ \text{Z} = \dfrac{\text{ρ} \times {N}_{A} \times a^{3}}{M} \\ = \dfrac{2.75 \times 6.023 \times {10}^{23} \times {( 654 \times {10}^{- 10} )}^{3}}{119}\end{array}

∴Z≃4Sofccunitcell∴ \text{Z} ≃ 4\text{S}\text{o}\text{f}\text{c}\text{c}\text{u}\text{n}\text{i}\text{t}\text{c}\text{e}\text{l}\text{l}

In FCC 1 atm surrounded by 6 atoms so coordination number is 6.
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