The characteristics of a water sample are as follows: $\mathrm{Na}^{+}=92 \mathrm{mg} / \mathrm{L}$, $\mathrm{K}^{+}=19.5 \mathrm{mg} / \mathrm{L}, \mathrm{Ca}^{2+}=40 \mathrm{mg} / \mathrm{L}$, and $\mathrm{Mg}^{2+}=24 \mathrm{mg} / \mathrm{L}$. What is the sodium adsorption ratio (SAR) of the water sample which may be considered for irrigation purposes?
[Atomic weight $(\mathrm{g} / \mathrm{mol}): \mathrm{Na}=23, \mathrm{~K}=39, \mathrm{Ca}=40$, and $\mathrm{Mg}=24$ ]
- $2.8$
- $1.9$
- $2.0$
- $4.00$
