O2 is considered 2 atoms because O2 is 2 oxygen atoms.
None of the diagrams you attached shows the scenario accurately,
or at all.
Heat flows from Object-B to Object-A, until both objects are at
the same temperature, somewhere between 10°C and 29°C.
I am not 100% sure but i think it is true.
You would most likely be witnessing an eclipse
Answer:

Explanation:
Given:
Gravity of Mars = 0.38 times the gravity at Earth
Gravity of Earth is, 
Radius of Mars (R) = 3400 km
Mass of mars (M) = ?
We know that, the acceleration due to gravity of a planet of mass 'M' and radius 'R' is given as:

Now, as per question:

Plug in 9.8 for
and solve for
. This gives,

Now, plug in this value in the above equation and solve for 'M'. This gives,

Therefore, the mass of Mars is
.