Explanation:

The decadal population growth rate of India grew consistently till 1971 and declined after that after peaking at 24.86%.
Work is defined as participation in any economically productive activity with or without compensation, wages or profit. Such participation may be physical and/or mental in nature. Work involves not only actual work but also includes
a. effective supervision and direction of work;
b. part time help or unpaid work on farm, family enterprise or in any other economic activity; and
c. cultivation or milk production even solely for domestic consumption.
Accordingly, as per Census of India, all persons engaged in 'work' defined as participation in any economically productive activity with or without compensation, wages or profit are workers. The Reference period for determining a person as worker and non-worker is one year preceding the date of enumeration.
The Census classifies Workers into two groups namely, Main workers and Marginal workers. Main Workers are those workers who had worked for the major part of the reference period i.e. 6 months or more (183 days). Marginal Workers are those workers who had not worked for the major part of the reference period i.e. less than 6 months.