The biosphere is:

The conversion of hydroxyapatite occurs due to the presence of $F^{-}$ ions in water. The correct formula of hydroxyapatite is:

Which of the following methods can be used to control water pollution?

Identify the true $(T)$ and false $(F)$ statements regarding the disease known as fluorosis:
$(1)$ Fluorosis weakens teeth and bones.
$(2)$ Fluorosis is caused by fluoride concentrations greater than $2 \ ppm$ $(2 \ mg/L)$.
$(3)$ Fluorosis causes neuromuscular disorders.
$(4)$ Fluoride deficiency causes fluorosis.

Which of the following molecules react with haemoglobin of the blood to produce toxic effect?

Match the following:

List-$I$	List-$II$
$A$. Insecticide	$I$. $COD$
$B$. $K_2Cr_2O_7 / 50\% H_2SO_4$	$II$. $PAN$
$C$. Bleaching of clothes and paper	$III$. $Na_3AsO_3$
$D$. Eye irritant	$IV$. $BOD$
	$V$. $H_2O_2$

The correct answer is: