What is the cause of genetic erosion?

$A$ codon has a sequence of $\underline{A}$,and specifies a particular $\underline{B}$ that is to be incorporated into a $\underline{C}$. What are $\underline{A}, \underline{B}, \underline{C}$ ?
$\underline{A} \quad \underline{B} \quad \underline{C}$

Guttation is the result of

Two cylinders $A$ and $B$ fitted with pistons contain equal amounts of an ideal diatomic gas at $300 \ K$. The piston of $A$ is free to move while that of $B$ is held fixed. The same amount of heat is given to the gas in each cylinder. If the rise in temperature of the gas in $A$ is $30 \ K$,then the rise in temperature of the gas in $B$ is ..... $K$

The number of $p\pi-d\pi$ 'pi' bonds present in $XeO_3$ and $XeO_4$ molecules,respectively,are:

$A$ coin is tossed $n$ times. The probability of getting a head at least once is greater than $0.8$. Then,the least value of such $n$ is: