Answer
$1.26 \times 10^{-2}$M
Work Step by Step
Using relation $pH=-log[H^{+}]$ ...(1)
As we are given that $pH$ for lime use is 1.9.
Equation (1) becomes: $1.9=-log[H^{+}] \implies log[H^{+}]=-1.9$
Thus, $[H^{+}]=10^{-1.9} \approx 1.26 \times 10^{-2}$M
