Which of the following is commonly tested in oil samples?

Kinematic viscosity is a critical property commonly tested in oil samples as it quantifies the oil's resistance to flow. Understanding viscosity is essential for evaluating how well oil can lubricate machinery and function in various operating conditions. The kinematic viscosity of oil can change due to temperature variations, contamination, or degradation, which can significantly impact its performance.

In industrial applications, maintaining the appropriate viscosity is key to ensuring effective lubrication, reducing friction, and preventing wear in machinery. It's also crucial for the oil to flow adequately through systems, which is why testing for kinematic viscosity is standard practice.

Other properties such as temperature, pH levels, and electrical conductivity are important but do not play as direct a role in assessing the lubricating efficacy of oils as kinematic viscosity does. For instance, while temperature affects viscosity, it is not directly measured as a critical property of the oil samples themselves; pH levels are more relevant in the context of water and some minerals but less so for typical oils; and electrical conductivity mainly helps assess contamination or degradation rather than lubricant efficiency. Therefore, kinematic viscosity stands out as a primary property of focus in oil testing.