The optimum temperature for polymerisation in $PCR$ is $....$ while the enzyme responsible for the mentioned step can tolerate temperatures up to $....$. Select the correct option according to the blanks.

Given below are two statements:
Statement $I:$ The $\text{DNA}$ fragments extracted from gel electrophoresis can be used in the construction of recombinant $\text{DNA}$.
Statement $II:$ Smaller size $\text{DNA}$ fragments are observed near the anode while larger fragments are found near the wells in an agarose gel.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following is required for the amplification of a gene of interest by $PCR$?

Describe the role of $CaCl_2$ in the preparation of competent cells.

Which impurities are released along with $DNA$ when cells are broken down for $DNA$ isolation?

Select the correct statements from the following: