The answer is 1. Radiation
Answer:
by exploring space then they saw them
The first one he discovered gravity when the apple fell on his head
Answer : The mass of helium gas added must be 12.48 grams.
Explanation : Given,
Mass of helium (He) gas = 6.24 g
Molar mass of helium = 4 g/mole
First we have to calculate the moles of helium gas.

Now we have to calculate the moles of helium gas at doubled volume.
According to the Avogadro's law, the volume of gas is directly proportional to the number of moles of gas at same pressure and temperature. That means,

or,

where,
= initial volume of gas = V
= final volume of gas = 2V
= initial moles of gas = 1.56 mole
= final moles of gas = ?
Now we put all the given values in this formula, we get


Now we have to calculate the mass of helium gas at doubled volume.


Therefore, the mass of helium gas added must be 12.48 grams.
Answer:
The flask would probably feel cooler than before the reaction started.
Reasoning:
Endothermic is a process or reaction accompanied by or requiring the absorption of heat