The environment is said to be unstable when the:
1
ELR (Environmental lapse rate) is more than the ALR (Adiabatic lapse rate)
2
ELR (Environmental lapse rate) is same as the ALR (Adiabatic lapse rate)
3
ELR (Environmental lapse rate) is less than the ALR (Adiabatic lapse rate)
4
ELR (Environmental lapse rate) is zero