Number of instantaneous reactions from the following is ______ .

$\mathrm{HCl}+\mathrm{NaOH}\to \mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}$

$2{\mathrm{H}}_{2\left(\mathrm{g}\right)}+{\mathrm{O}}_{2\left(\mathrm{g}\right)}\stackrel{25°C}{\to } 2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}$

${\mathrm{AgNO}}_{3\left(\mathrm{aq}\right)}+{\mathrm{NaCl}}_{\left(\mathrm{aq}\right)}\to {\mathrm{AgCl}}_{\left(\mathrm{s}\right)}\downarrow +{\mathrm{NaNO}}_{3\left(\mathrm{aq}\right)}$is precipitation reaction.

Both neutralization and precipitation reactions are the example of instantaneous reaction. Because these two reactions can occur very fast through ions in the solution.