I believe it can be warm because usually the surface below us is warm itself, causing the air to be warm as well. The temperature can vary as well
Answer to this is Radioactive isotopes.
Isotopes are the species of the same element having different atomic masses that means the number of protons remains the same but number of neutrons do differ. For example
and
are the two isotopes of Hydrogen (
).
Radioactive isotopes are the isotopes which release some kind of energy in the form of alpha particles, beta particles or gamma radiation. Examples of each of the decay processes are :
Alpha Decay: In this decay one alpha particle having atomic mass 4 and atomic number 2 or we can say a He molecule will come out. 
Beta Decay: In this decay a
particle is emitted increasing the atomic number of the reactant by 1 unit.

Gamma Radiation: In this type of reaction only radiation is emitted out which does not change the original molecule.

Answer:
2.7724 g
Explanation:
Mass of pre- 1892 pennies = 3.1 g
Abundance = 45.4 %
Mass of post 1892 pennies = 2.5 g
Abundance = 100 - 45.4 = 54.6 %
The average mass is given as = ( 3.1 g * 45.4 / 100) + (2.5g * 54.6 / 100)
Average Mass = 3.1 * 0.454 + 2.5 * 0.546
Average Mass = 1.4074 + 1.365 = 2.7724 g
A MOLECULE IS MADE OF TWO OR MORE ELEMENTS CHEMICALLY COMBINED IS KNOWN AS A COMPUND.
A MOLECULE IS MADE OF TWO ATOMS IS JUST AN ELEMENT.
A MOLECULE MADE OF TWO OR MORE ELEMENTS IS KNOWN AS A COMPUND.
<h3><u>Answer;</u></h3>
- Molecules along the surface of a liquid behave differently than those in the bulk liquid.
- Cohesive forces attract the molecules of the liquid to one another.
- Surface tension increases as the temperature of the liquid rises
<h3><u>Explanation;</u></h3>
- Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area. The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules.
- A molecule in the bulk liquid experiences cohesive forces with other molecules in all directions, while a molecule at the surface of a liquid experiences only net inward cohesive forces.
- Surface tension decreases when temperature increases because cohesive forces decrease with an increase of molecular thermal activity.