The number of people who are qualified to work and who offered themselves for employment are called

The correct term for the number of people who are qualified to work and who offer themselves for employment is the working population.
The working population refers to the subset of the total population that is actively engaged or seeking employment. It includes individuals who are qualified, available, and willing to work. This encompasses both employed individuals and those who are actively looking for work, such as job seekers.
The working population is an important measure for understanding the labor market. It helps policymakers, businesses, and economists in assessing the job market's health and determining factors such as employment rates, labor force participation, and unemployment rates.
Options like "mobility of labor" and "migrant labor" focus on the movement of workers between different locations, which is a related concept but not the same as the total number of qualified individuals available for employment. "Labor turnover" refers to the rate at which workers leave and join a particular company or industry, which is also not synonymous with the working population as a whole.
Therefore, the working population is the term that correctly describes the number of qualified individuals who are available for employment.