Ammonium chloride crystallizes in a body centered cubic lattice with edge length of unit cell equal to 387 pm.  If the size of chloride ion is 181 pm, the size of NH4+ ion would be

Given, Edge length of units cell, a = 387 ppm Radius of Chloride ion, rCl-=181 pmRadius of NH4+ ion, 1NH4+ = ?Body center cube ,BCC    2(r++r−)=a3⇒r++r−=a32⇒rNH4++rCl-=a32⇒rNH4++181=387×1.7322∴  rNH4+=154