Which of the following is a Dobereiner's triad?

Which of the following is a method of plant tissue culture?

For all real $x$,the minimum value of the function $f(x)=\frac{1-x+x^2}{1+x+x^2}$ is

Which of the following carbonyl compounds will exhibit enolization?
$(i)$
$(ii)$
$(iii)$
$(iv)$
$(v)$

The organization of living organisms starts with which level?

Let $S$ be the sample space of the random experiment of throwing simultaneously two unbiased dice with six faces (numbered $1$ to $6$) and let $E_k = \{(a, b) \in S : ab = k\}$ for $k \geq 1$. If $p_k = P(E_k)$ for $k \geq 1$, then which of the following is correct?