Because it is flammable and also the lightest of all gases which means if a balloon is filled up with hydrogen gas the balloon won't stop going up until the expansion due to heat from the sun causes it to pop at really high altitude eg20000 feet now put that type of info in example tourist specialised transport balloons it will be deadly and that is why they use hot air not gases such as hydrogen but if it was a party balloon it wouldn't be of any help because when you lose your balloon it's gone for good

Takes shape of the container
Is one of the fire triangle main character
It has 23% of the air occupancy in the atmosphere

Electrons protons neutrons

Because humans on the verge of exploitation and production the remains by products can sometimes be too contaminated for further use eg nuclear energy production leads to radioactive waste which is pretty dangerous and at the same time hard to get rid of we know nowadays that modern agricultural methods of production help to sustain enough yield for consumption but at the same time altering natural biological evolutions which may lead to a mutation or to the failure of the project since gene editing or gene modification can be lethal at certain stages

And it still does because the yellow sun is changing to become a red giant our star

Pluto isn't a planet anymore so I am going with Mercury and Venus since they are the smallest planets due to their distance from the sun which deformed a lot of matter

We are a bit neutral because if you say humans live out of the earth most people will assume outer of the planet completely in the vaccuum of space but when we say humans live in the earth some will assume we Co exist in the interior of the earth in the core that is a tricky question depends on how it is asked

I am guessing mpt is melting point 0°cand but Is boiling point 100°c