Which main sequence star would be least luminous- G1 G5 G9 F0 F3?

Among the given main sequence stars, the G9 star would be the least luminous. The classification indicates that G-type stars (like G1 and G5) are more luminous than G9 stars, and F-type stars (F0 and F3) are even more luminous than G-type stars. Therefore, as the spectral class moves from G1 to G9, the luminosity decreases, making G9 the least luminous option.