Answer :
The edge length of the unit cell in NaCl is 552 pm, calculated by adding the radii of Na+ (95 pm) and Cl- (181 pm) and multiplying by 2.
Therefore, the correct answer to the question is: D. 552
To calculate the edge length of the unit cell in NaCl, which crystallizes in a face-centered cubic (FCC) structure, we must consider the arrangement of the ions. In the NaCl structure, each sodium ion is surrounded by six chloride ions, and each chloride ion is surrounded by six sodium ions, forming an octahedral geometry. At each edge of the unit cell, we find half of a Na+ ion's radius and half of a Cl− ion's radius. Therefore, the edge length of the unit cell is twice the sum of the radii of Na+ and Cl−, which are 95 pm (picometers) for Na+ and 181 pm for Cl−.
The calculation is as follows:
Edge length = 2 × (Radius of Na+ + Radius of Cl−)
Edge length = 2 × (95 pm + 181 pm) = 2 × 276 pm
= 552 pm.
Therefore, the correct answer is D. 552 pm, representing the edge length of the unit cell in NaCl.
