Refer to the $1$H NMR of racemic $1-$phenylethylamine combined with $($S$)-(+)-$O$-$acetylmandelic acid, which results in the two diastereomeric salts. This NMR will be compared to your NMR of resolved $(-)-1-$phenylethylamine combined with $($S$)-(+)-$O$-$acetylmandelic acid. The highlighted methyl group in $1-$phenylethylammonium ion is closest to:

Question $14$ options:

$1$ ppm

$2$ ppm

$4$ ppm

$6$ ppm

$7$ ppm

$9$ ppm