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When air is warmed up, its molecules move faster and faster and as a
result they move further from each other. They still have the same
mass, but they now occupy a larger volume. This means that its density
is smaller.
The opposite when air is cooled off. The molecules slow down, get
closer together, occupy a smaller volume and therefore its density is
bigger.
When air is warmed up, it goes up. Once it's up there, is cools off and
goes back down. Near the heated surface the air gets warmed up again,
goes up, cools down, goes back down, and again and again.
that is called convection cells
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Answer:
The mass of copper = 208.26 grams.
Explanation:
Density = mass / volume
8.9 = mass / 23.4
mass = 8.9 * 23.4
= 208.26 grams.
Answer:
B. Excited state
Explanation:
Energy levels higher than the ground state are called the excited states. This concept is based on the premise that electrons can move round the nucleus in certain permissibe orbits or energy levels.
The ground state is the lowest energy state available to the electron. This is usually the most stable state.
The excited state is any level higher than the ground state. An electron in an energy level has a definite amount of energy associated with it at that level.
The answer should be A. CaO + CO2 —> CaCO3
Answer: C. The non metal
Explanation:-
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
The nomenclature of ionic compounds is given by:
1. Positive ion or metal is written first.
2. The negative ion or non metal is written next and a suffix is added at the end of the negative ion. The suffix written is '-ide'.
For example: 
, cesium is metal having an oxidation state of +1 called as 
cation and bromine 
is an anion with oxidation state of -1. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral called as cesium bromide.
