Giải thích các bước giải:

3, 

\(\begin{array}{l}
S{O_3} + {H_2}O \to {H_2}S{O_4}\\
N{a_2}O + {H_2}O \to 2NaOH\\
CaO + {H_2}O \to Ca{(OH)_2}\\
C{O_2} + {H_2}O \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} {H_2}C{O_3}
\end{array}\)

\({H_2}S{O_4}\): axit sunfuric 

\(NaOH\): natri hidroxyt

\(Ca{(OH)_2}\): canxi hidroxyt

\({H_2}C{O_3}\): axit cacbonic

4,

\(\begin{array}{l}
Zn + 2HCl \to ZnC{l_2} + {H_2}\\
{n_{Zn}} = 0,25mol\\
 \to {n_{HCl}} = 2{n_{Zn}} = 0,5mol\\
 \to {V_{HCl}} = \dfrac{{0,5}}{{0,5}} = 1l\\
{n_{{H_2}}} = {n_{Zn}} = 0,25mol\\
 \to {V_{{H_2}}} = 5,6l
\end{array}\)

Chúc cậu thi tốt!