your horn is most probably leaking. Check all keys in combination and alone, in particular, the G sharp or G# ( called also Sol diesis in some countries)

Put a light in the sax ( these says you have strips of led for almost no money) and observe in the dark.

Most probably you can’t fix leaks ( unless it is G# and unless this has regulation screws) your tech will.

 

the link between the high stack and the low stack seems to be at fault here...

 

When the lower octave-right-hand notes won't speak well, I always suspect the lower octave vent/system. DAVE

 

The G key is not closing one of he octave pips. It is probably an adjustment where the neck fits to the body. There should be a small space between the body lever and neck key.

 

As a beginner this could be an embouchure issue.

 

I am profound at stating the obvious, but a teacher could probably help here. S/He might know enough about saxes to know if this is the turn of a screw or a some time in a repair shop. Or, he/she could determine that there was a player issue.

 

Step One: Take in more mouthpiece, if that doesn't work then

Step Two: See a repairman, (have him or her test the horn with your mouthpiece.) if that doesn't work then

Step Three: Get a teacher that knows how to play the soprano saxophone until you can play every note on the horn.

 

But not in that order

 

Find some friend of yours or a person who's being playing for longer. Let him/her play your horn if the problem is still there it is a leak if not it's your embouchure. SIMPELSSS!!

 

I guess I did not think of the obvious.......do you have the mouthpiece pushed in enough to tune it to pitch? If you don't have a tuner, match it to a piano. Plan an F on the piano and see if G is in tune on the soprano. Remember that the soprano is a whole step above the piano notes.