$DNA$ acts as a template for the synthesis of which of the following?

In which of the following is the flow of genetic information in the reverse direction?

Genetic mapping of bacteriophage $\phi X174$ has been done by

Which of the following is an incorrect combination?

Which one of the following statements about the particular entity is true?

How many of the given statements $(i-iv)$ is/are correct?
$i.$ In transcription,adenosine pairs with uracil.
$ii.$ Regulation of lac operon by repressor is referred to as positive regulation.
$iii.$ The human genome has approximately $50,000$ genes.
$iv.$ Haemophilia is a sex-linked recessive disease.