The volume if voids of a rhombohedral array of spherical grains with α=75° is _______
a) 0.4266
b) 0.7439
c) 0.3895
d) 0.3595

Answer: c
Explanation: Given,
α=75°
The total volume V=(1-cosα)*(√(1+2cosα))
V=(1-cos75°)*(√(1+2cos75°))
V=0.9131
Volume of the solids V_s=(π/6)=0.5236
Volume of the voids V_v=V-V_s=0.9131-0.5236
V_v=0.3895.