It should be A since it needs external source of heat to thrive
while endotherm can produce it's own preferable heat.
The piece of evidence would suggest an unknown substance is an ionic compound is that it conducts electricity when dissolved in water.
The reaction is
2H₂(g) + O₂(g) ---> 2H₂O
Thus as per balanced equation two moles of hydrogen will react with one moles of oxygen.
There is a directly relation between moles and volume. [One mole of each gas occupies 22.4 L of volume at STP]
Thus we can say that two unit volume of hydrogen will react with one unit volume of oxygen
Now as we have started with equal units of volume of both oxygen and hydrogen, half of oxygen will be consumed against complete volume of hydrogen
so the gas which will remain in excess is oxygen
I do believe its is A. all types of plants
