This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
For measuring hardness of Co-Cr alloy, which hardness test is used? 
Select and explain. 
A. Vicat apparatus, B. Cold bend, C. Heat and cold bend, D. Rockwell hardness test
D: Rockwell hardness test
Answer: D: Rockwell hardness test 
Explanation: 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