Answer:
1750
Explanation:
Greenhouse gases are those gases that are believed to contribute to the rise in the temperature of the earth by trapping infrared rays close to the surface of the earth.
Prominent among the greenhouse gases are; N2O, methane and CO2.
From the chart, we can see that the lowest sum of concentration of greenhouse gases measured in ppm was obtained in 1750. Thus this period shows the lowest composition of greenhouse gases.
