The anions (A) from hexagonal close packing and atoms (M) occupy only two-third of the octahedral voids. The general formula of the compound is


Correct option is



In hexagonal close packing on sphere is in contact with 12 sphere. Thus,

The number of anion A pre unt cell = 12

Octahedral voids = Number of sphere = 12 

∴  No. of M atoms per unit cell  of octahedral voids 


                                                    = 8 

⇒                  A : M = 12 : 8 = 3 : 2

∴  The formula of the compound is M2A3.



The X-ray power pattern of potassium chloride shows a cone at θ = 90o, using X-ray of wavelength 1.54 × 10–8 cm. What is the spacing between the planes?      


When an electron in an excited Mo atom falls from L to K, shell, an X-ray is emitted. These X-ray are diffracted at angle of 7.75 by planes with a separation of 2.64 Å. What is the difference in energy between K-shell and L-shell in Mo assuming a first order diffraction (sin 7.75 = 0.1349)?


A compound formed by elements A and B crystallises in cubic structure where B atoms are at the corner of a cube and A atoms at the face centre. The formula of the compound is    


Match box belongs to


In a crystalline solid, having formula AB2O4, oxide ions are arranged in cubic close packed lattice while cations A are present in tetrahedral voids and cations B are present in octahedral voids. The percentage of tetrahedral voids occupied by A is     


Ag metal crystallises in a cubic closest packed arrangement with the edge of the unit cell having a length a = 407 pm. The radius of the similar atom is 


The density of solid argon is 1.65 g/mL at –233oC. If the argon atom is assumed to be sphere of radius 1.54 × 10–8 cm, what percentage of solid argon is apparently empty space?(At wt of Ar = 40).


A compound CuCl has fcc structure. Its density is 3.4 g cm–3, what is the length of unit cell?


A metal crystallizes into two cubic phases fcc and bcc whose unit cell lengths are 3.5 and 3.0 Å respectively. What is the ratio of densities of fcc and bcc?


The radius of a divalent cation M2+ is 94 pm and that of divalent anion X2–is 146 pm. Thus, M2+ X2– has