Which one of the following is not an essential mineral element for plants while the remaining three are?

The number of non-empty subsets of the set $\{1, 2, 3, 4\}$ is:

The half-lives of two radioactive nuclides $A$ and $B$ are $1 \ min$ and $2 \ min$ respectively. Equal weights of $A$ and $B$ are taken separately and allowed to disintegrate for $4 \ min$. What will be the ratio of weights of $A$ and $B$ disintegrated?

What is the time (in $sec$) required for depositing all the silver present in $125 \ mL$ of $1 \ M \ AgNO_3$ solution by passing a current of $241.25 \ A$? $(1 \ F = 96500 \ C)$

The wavelength of radiation emitted is $\lambda_0$ when an electron jumps from the third to the second orbit of a hydrogen atom. For the electron to jump from the fourth to the second orbit of the hydrogen atom,the wavelength of radiation emitted will be

Which of the metabolites is common to respiration-mediated breakdown of fats,carbohydrates,and proteins?