Answer:
...................................................
The correct balanced chemical equation which occur when methane burn in oxygen gas is
CH4 + 2O2 --> 2H2O +CO2 (answer D)
when methane is burned in presence of oxygen gas it produces carbon(IV) oxide and water and energy,that is 1 mole of CH4 reacted with 2 moles of O2 to form 2 moles of water and 1 mole of CO2 and enegy. This energy make the methane to be used as fuel.
Answer : The time required for decay is, 84 days.
Explanation :
Half-life of chromium-51 = 28 days
First we have to calculate the rate constant, we use the formula :



Now we have to calculate the time required for decay.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant
t = time taken by sample = ?
a = let initial activity of the sample = 100
a - x = amount left after decay process = 12.5
Now put all the given values in above equation, we get


Therefore, the time required for decay is, 84 days.
Photosynthesis is the process by which plants create their food. It involves the operation of enzymes in the plant cells , and they work best at certainpH levels. ... Thus, as the plant's pH drifts away from the best pH, the rate of photosynthesis will decrease.