For measuring hardness of Co-Cr alloy, which hardness test is used?
(A) Vicat apparatus (B) Cold bend (C) Heat and cold bend (D) Rockwell hardness test
(D) The Vicat apparatus is commonly used to measure the initial setting time of gypsum products. 
A method for the measurement of ductility is known as the cold bend test.
Rockwell Hardness Number (RHN) Like the Brinell hardness test, a steel ball or a conical diamond point is used. However, instead of measuring the diameter of the impression, the depth is measured directly by a dial gauge on the instrument. 

Application: The Rockwell test has a wider application for materials, since Brinell test is unsuitable for brittle materials as well as plastic materials.
Ref- Mannapallil BASIC DENTAL MATERIALS  P:24