$t-RNA$ is also known as?

$DNA$ exists in a double-stranded form whereas $RNA$ is mainly a single-stranded molecule. What is the likely reason for $DNA$ being double-stranded?

The three-dimensional structure of the $t-RNA$ molecule is . . . . . . .

What is the length of one full turn of the $DNA$ helix?

What does $t-RNA$ look like?

Which one of the following statements about Histones is wrong?