Bamboo and grasses elongate by the activity of ......

Choose the incorrect statement from the following:
$S1:$ The efficiency of a heat engine can be $1$,but the coefficient of performance of a refrigerator can never be infinity.
$S2:$ The first law of thermodynamics is basically the principle of conservation of energy.
$S3:$ The second law of thermodynamics does not allow several phenomena consistent with the first law.
$S4:$ $A$ process,whose only result is to transfer heat from a colder to a hotter object,is impossible.

The half-life period of a radioactive element $X$ is the same as the mean lifetime of another radioactive element $Y$. Initially, both of them have the same number of atoms. Then:

In an entrance test,there are multiple-choice questions. There are four possible answers to each question,of which one is correct. The probability that a student knows the answer to a question is $90\%$. If he gets the correct answer to a question,then the probability that he was guessing is:

The molecular formula of diphenylmethane is $C_{13}H_{12}$. How many structural isomers are possible when one of the hydrogen atoms is replaced by a chlorine atom?

Helium mixed with oxygen is used in the treatment of