# According to central pollution central board (CPCB) which size of particulate matter are responsible for causing the greatest harm to human health?

$\begin{array}{1 1}(a)\;2.5\mu m\;or\;less\\(b)\;3.5\mu m\;or\;less\\(c)\;4.5\mu m\;or\;less\\(d)\;5.5\mu m\;or\;less\end{array}$

Solution :
The particular matter of 2.5 or less in size are inhaled deep into the respiratory tract (up to lungs) and causes respiratory problems and may even lead to death.
$2.5\mu m\;or\;less$
Hence (a) is the correct answer.
edited Nov 2, 2017 by meena.p