The correct answer is (a). Increase in the size of working population.
The other options are all adverse effects of population growth in an economy.
(b) Reduced size of holdings: As the population grows, the demand for land increases. This can lead to a reduction in the size of individual land holdings, which can make it difficult for farmers to make a living.
(c) Increasing unemployment: As the population grows, the number of people looking for work also increases. This can lead to higher unemployment rates, which can have a negative impact on the economy.
(d) Reduced per capita availability of food grains: As the population grows, the demand for food also increases. This can lead to a reduction in the per capita availability of food grains, which can have a negative impact on the health of the population.
(a) Increase in the size of working population: This is not necessarily an adverse effect of population growth. In fact, a larger working population can be a positive thing, as it can lead to increased economic output. However, it is important to ensure that the working population is properly educated and trained, so that they can contribute to the economy in a meaningful way.