List any three human activities which would lead to an increase in the carbon dioxide content of air.
The following activities of human beings may increase carbon dioxide content of air:
(i) Burning of fossil fuels such as petrol, diesel and coal in various activities like transportation and industrial processes.
(ii) Burning of wood and charcoal for heating, cooking, etc.
(iii) Deforestation that reduces the green plant and tree population, consequently utilisation of atmospheric CO2 during photosynthesis.