The technique used to make numerous copies of a specific segment of $DNA$ quickly and accurately is

In which of the following molecules/ions are all the bonds not equal?

$A$ ball of mass $m_1$ and another ball of mass $m_2$ are dropped from the same height. If the time taken by the balls to reach the ground is $t_1$ and $t_2$ respectively,then:

If $\overrightarrow{a}=\hat{i}+\hat{j}+\hat{k}$,$\overrightarrow{b}=\hat{i}+\hat{j}$,$\overrightarrow{c}=\hat{i}$ and $(\overrightarrow{a} \times \overrightarrow{b}) \times \overrightarrow{c}=\lambda \overrightarrow{a}+\mu \overrightarrow{b}$,then $\lambda+\mu$ is equal to:

An animal phylum having radially symmetrical adults but bilateral symmetrical larvae is

The point collinear with $(1, -2, -3)$ and $(2, 0, 0)$ among the following is