According to Central Pollution Control Board (CPCB), which particulate size in diameter ( in micrometers ) of the air pollutants is responsible for greatest harm to human health ?

Question

$\begin {array} {1 1} (1)\;5.2-2.5 & \quad (2)\;2.5\: or\: less \\ (3)\;1.5\: or\: less & \quad (4)\;1.0\: or\: less \end {array}$