The concentration of fluoride, lead, nitrate and iron in a water sample from an underground lake was found to be $1000\;ppb, 40\;ppb, 100\; ppm$ and $0.2\;ppm$, respectively. This water is unsuitable for drinking due to high concentration of :

Question

$\begin{array}{1 1} (1) Fluoride \\ (2) Lead \\ (3) Nitrate \\ (4) Iron \end{array} $