List of top Environmental Chemistry Questions asked in GATE Environmental Science and Engineering

A saturated \(CaCO_3 \)stock solution is existing at 25°C. In one experiment (i) 25 g \(Na_2CO_3 \)is added to the stock solution. In another experiment (ii) 25 g \(Na_2SO_4\) is added to the stock solution. Select the correct statement from the following.
In a region, total annual consumption of gasoline is 30.6 million tons. The land required for growing sugarcane to produce enough bioethanol to replace the gasoline completely is ___________ \(km^2\) (an integer value). 
Ethanol energy equivalent is 67% of gasoline, gasoline density is 850 \(kg/m^3\), yield of bioethanol produced from sugarcane per hectare of land is 3750 L, and 1 \(km^2\) = 100 hectares
Initially a bottle contained 400 g of ethanol. Half of ethanol was used by a student for preparing the stock solution in an environmental chemistry laboratory just before summer vacation of 90 days. After completing the procedure, the student left the bottle uncorked. If the unsealed bottle losses ethanol at a rate of 0.5 g/day, the ethanol that will be left in the bottle at the end of the summer vacation is __________ g (an integer value).
The pH of a solution containing 0.1M of acetic acid and 0.05 M of sodium acetate is ________ (rounded off to 2 decimal places).
The $pK_a$ value of ionization of acetic acid is 4.76.
The ionic strength of a solution containing 0.01M of $CaCl_2$ and 0.001M of $Na_2SO_4$ is _____ M (rounded off to 3 decimal places)
The Streeter-Phelp's oxygen sag equation for a river is based on a few assumptions. The correct assumption(s) is/are
The concentration of Ozone corresponding to a mixing ratio of 120 ppbv at pressure of 1 atmosphere and temperature of 25°C is ________ \(μg/m^3\) (rounded off to 1 decimal place).
Atomic weight of oxygen = 16; R= 8.314 J/K-g.mole.
Which one of the following conversions belongs to nonsymbiotic nitrogen fixation?
The environmental temperature increases by 6°C/km with height at a particular location. The stability condition of the atmosphere at the location is ______,
The maximum coordination number of $Sn^{4+} is _____.
Hardness in water is NOT caused by ______