Answer:
1. D. They can be a substance, material, object or source of energy.
2. B. The properties will be different.
3. C. When two reactants form one product, the reaction is spontaneous.
This should be valence electrons. They determine the chemical properties of an atom.
Answer:
To the right relative to the original frame.
Explanation:
In first reference frame <em>S</em>,
Spatial interval of the event, 
Temporal interval of the event, 
In the second reference frame <em>S'</em>, the two flashes are simultaneous, which means that the temporal interval of the event in this frame is 
The speed of the frame <em>S' </em>with respect to frame <em>S</em> = v.
According to the Lorentz transformation,

And positive v means the velocity of the second frame<em> </em><em>S'</em> is along the positive x-axis direction, i.e., to the right direction relative to the original frame <em>S</em>.
CO2 or carbon dioxide. You breathe it out and it is one of the greenhouse effects gasses that need to be limited.