Given, cytosine=20%
\(\therefore \) Percentage of Guanine=20%
Now according to Chargaff's rule, A+T=100-(G+C)
=> A+T=100-40
\(\therefore \) Percentage of Thymine=percentage of Adenine
 =\(\frac { 60% }{ 2 } \)% = 30%

The statement is correct.Because of degeneracy codons, mutations at third base of usually do not result into any change in phenotype.On the other hand, if codon is changed in a way that now it specifies another  amino acid it may alter the protein function as it happens in case of \(\beta \) - globulin of haemoglobin, protein where a substitution of valine instead of glutamic acid causes changes in its structure and function, and resulting into sickle-cell trait.

(i) The methylated guanosine cap helps in the binding of mRNA to the smaller subunit of ribosome during initiation of translation.
(ii) Poly-A tail has a direct relatioship with the logevity of mRNA.

1. DNA polymerase can polymerise the nucleotides only in 5' -> 3' direction.
2. Hence on the template strand of DNA with 5' -> 3' polarity there is discountinuous synthesis.
3. These short stretches of DNA are joined together by DNA-ligase into a new strand of DNA.

1.The presence of 2'OH-group of ribose makes RNA more labile and prone to degradation.
2.In the heat-killed S-strain,it would not have remained functional and hence would not have transformed the R-cells into S-cells.