Which one of the following is not observed in biodiversity hotspots?

If $\triangle ABC$ is right-angled at $A$,then $r_2+r_3$ is equal to

If $\lim _{x \rightarrow 0}\left(\frac{\cos 4 x+a \cos 2 x+b}{x^4}\right)$ is finite,then the values of $a, b$ are respectively :

The number of subsets of $\{1, 2, 3, \ldots, 9\}$ containing at least one odd number is

Deficiency of micronutrients not only affects plant growth but also disrupts their specific functions,such as photosynthesis and mitochondrial electron transport. Which of the following groups of three minerals disrupts photosynthesis and mitochondrial electron transport?

Which of the following substances has the highest melting point?