A balloon filled with helium does not rise in air indefinitely but halts after a certain height. (Neglect winds). Explain

A baloon filled with helium rises against gravity increasing its potential energy. The speed of the baloon also increases as it rises. How do you reconcile this with the law of conservation of mechanical energy ? You can neglect viscous drag of air and assume that density of air is constant.

Why gas filled balloons rise up, only to a certain height ?

A balloon filled with helium rises to a certain height at which it gets fully inflated to a volume of 10^(5) litres. If at this altitude, temperature and atmospheric pressure are 268 K and 2xx10^(-3) atm respectively, what weight of helium will be required to fully inflate the balloon ?

A balloon filled with helium or hot air can float in the atmosphere. A balloon filled with air from your lungs falls to the ground when it is released. Why do these balloons behave differently?

Statement-1: A gas filled balloon stops rising after it has attained a certain height in the sky. Statement-2: At the highest point the density of air is such that the buoyant force on the balloon just equals its weight.

Statement I: A hydrogen-filled balloon stops rising after it has attained a certain height in the sky. Statement II: The atmospheric pressure decreases with height and becomes zero when the maximum height is attained.