Most suitable method of introducing alien $DNA$ into a plant cell is

If $f: N \rightarrow Z$ is defined by $f(n)=\begin{cases} 2 & \text{if } n=3k, k \in Z \\ 10 & \text{if } n=3k+1, k \in Z \\ 0 & \text{if } n=3k+2, k \in Z \end{cases}$,then $\{n \in N: f(n)>2\}$ is equal to

The electron in a hydrogen atom makes a transition from an excited state to the ground state. Which of the following statements is true?

Three concentric metallic spherical shells of radii $R, 2R, 3R$ are given charges $Q_1, Q_2, Q_3$ respectively. It is found that the surface charge densities on the outer surfaces of the shells are equal. Then,the ratio of the charges given to the shells,$Q_1 : Q_2 : Q_3$ is

The graph which represents the variation of mean kinetic energy of molecules with temperature $t^{\circ}C$ is

The $pH$ of water is $7$. When a substance $Y$ is dissolved in water,the $pH$ becomes $13$. The substance $Y$ is a salt of