Potassium can be used as :
fertilizer in biological sysytem
soft soap (KOH)
absorbant of CO2
all of these
Potassium uses -
1. In the biological system as fertilizer.
2. Potassium hydroxide in soft soap
3. Excellent absorbent of CO2
Potassium can be used as all given options.
Therefore, option(4) is correct.