Which statements about the generation of electrophiles are correct?

1. Aoleum supplies $\mathrm{SO}{}_3$ as the electrophile for sulfonation
2. B$\mathrm{HNO}{}_3+2\mathrm{H}{}_2\mathrm{SO}{}_4\to \mathrm{NO}{}_2{}^{+}+\mathrm{H}{}_3\mathrm{O}{}^{+}+2\mathrm{HSO}{}_4{}^{-}$ describes formation of the nitronium ion
3. Can acid chloride $\mathrm{RCOCl}$ with $\mathrm{AlCl}{}_3$ gives the acylium ion $\mathrm{RCO}{}^{+}$
4. D$\mathrm{CH}{}_3\mathrm{Cl}$ with $\mathrm{AlCl}{}_3$ gives a long-lived free $\mathrm{CH}{}_3{}^{+}$ ion that is as stable as $(\mathrm{CH}{}_3){}_3\mathrm{C}{}^{+}$