$ 7.30 \;g $ of hydrochloric gas (pure $HCl $) are dissolved in water to form $10\%$ hydrochloric acid. To calculate the pH, first calculate the number of moles of $ HCl $:
$n_{HCl}$ $=$ $\frac{m_{HCl}}{M_{HCl}}$ $=$ $\frac{7.30}{36.5}$ $=$ $0.20\; mol $
Then we calculate the molarity of $HCl$:
$[HCl]$ $=$ $\frac{n_{HCl}}{V}$ $=$ $\frac{0.20}{10}$ $=$ $0.020\frac{mol}{L}$
Finally, we calculate the pH:
$pH$ $=$ $-log[HCl]$ $=$ $-log0.020$ $=$ $1.70$
