Question

The normal graphite structure has coordination number 3, however on typical transformation u at applied pressure and temperature it becomes diamond with a coordination number of_______

(a) 2

(b) 3

(c) 4

(d) 5

The question was asked by my school principal while I was bunking the class.

This interesting question is from High Pressure and Hydrothermal Methods topic in section Preparative Methods of Solid State Chemistry

Answer 1

Correct answer is (c) 4

The best I can explain: Phases synthesized at high pressures tend to have higher densities than phases synthesized at atmospheric pressure and this sometimes gives rise to unusually high coordination number hence at 130 kbar pressure and 3000◦C graphite undergoes transformation and becomes diamond with coordination number 4.