Some time ago I tested it and 25 grams of SN dissolved in 50ml of water. I didn't see any undissolved parts.
Of course I didn't drink it
However if you see any undissolved parts of SN you can add water very gently until all SN is dissolved.
The standard dose of SN is 25 grams.
35 grams for people over 100 kilograms.
Of course in a dose of 35 grams of SN, 50ml of water will most likely be too little to dissolve all SN.
In this picture you sent the doses are a bit smaller. I don't know if it's better or not.
Most likely 20 grams as a standard dose is enough, but don't take my words as an oracle.