Explanation:
Sublimation is defined as a process in which solid state of a substance directly changes into vapor or gaseous state without undergoing liquid phase.
For example, naphthalene balls show sublimation at room temperature.
As this process does not cause any change in chemical composition of a substance. Hence, it is known as a physical process.
Similarly, when 
sublimes readily at 
. This shows change in physical state of carbon dioxide is taking place, i.e, from solid to gaseous phase.
Thus, we can conclude that when sublimes readily at then it means physical properties are usually associated with a compound that undergoes this kind of change.
Answer:
the advantages of modern periodic tables are given below and explained.
- position of hydrogen:since hydrogen has the least atomic number i.e 1 ,it is kept in group 1 of modern periodic table, but still controversial due to its. dual characteristics since it shows the characteristics of borh group 1 and group 17.
- position of isotopes :isotopes are element having the same atomic number but different atomic weight . Without any doubt all isotopes of one element and kept in one place.
- position of lanthanide and acnitinides: element of Lanthanides series and element of Actinides series are kept below the main block of the periodic table as they have different properties from other elements.
- correction of periodic law: some elements do not obey mendeleev periodic law , but when they are arranged according to atomic number they obey the modern periodic law.
- position of alkali metals and coinage metals : in modern periodic table , alkali metal are kept in group IA and coinage metals are in group.
hope this helped you☺️
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actually as I say these points say that the modern periodic table is better than mendeleev periodic table so, don't get confused.
answer is A
The kinetic theory is used to explain the behaviour of gases.
One of the assumptions states that "a gas is composed of a large number of identical molecules moving at different speeds".
Answer: The correct answer is the option: B. An element with eight valence electrons is chemically unstable.
Explanation:
Hello! Let's solve this!
We will analyze each of the options:
A. The group number of the element provides a clue to the number of valence electrons: it is correct, since it provides the number of valence electrons.
B. An element with eight valence electrons is chemically unstable: this is not correct, since elements with eight electrons in the valence shell cannot react because they already have the last complete shell. Therefore, they are chemically stable.
C. The points must be placed one at a time on each side of the chemical symbol: it is correct, because that is the way to make the point diagram.
D. An atom is chemically stable if all the points are paired: this is correct since this verifies that the point diagram has been done well.
We conclude that the correct answer is the option: B. An element with eight valence electrons is chemically unstable.
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