Which of these digital modes has the narrowest bandwidth?

FT8 is designed to be an incredibly narrowband and efficient mode. It uses 8-tone frequency-shift keying with tones spaced exactly 6.25 Hz apart. This results in a total signal bandwidth of only 50 Hz, which is the narrowest among the given choices. For comparison, a standard 170 Hz shift RTTY signal occupies about 250 to 300 Hz of bandwidth. MFSK16 occupies roughly 316 Hz, and PACTOR IV is a comparatively wideband mode that can use up to 2400 Hz of bandwidth to achieve high data transfer rates.