1- The correct answer is C :
the elements arranged in the modern periodic table by increasing atomic number.
The explanation:
-The elements in the periodic table are arranged to increase the atomic number. All of these elements display several other trends and we can use the periodic law and table formation to predict their chemical, physical, and atomic properties.
2- The correct answer is C:
strontium, magnesium, calcium, beryllium are the elements which have similar properties.
The explanation:
-strontium, magnesium, calcium, beryllium, these belong to the alkaline earth metal group.
Because the outer electron structure in all of these elements is similar, they all have somewhat similar chemical and physical properties
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3- The correct answer is A :
Potassium
The explanation:
-The elements potassium and sodium have similar chemical properties because they have the same number of valence electrons and form +1 ions.
4- The correct answer is D
The explanation:
Mendeleev didn't include helium, neon, and argon in his periodic table because these elements had not yet been discovered.
5- The correct answer is B:
The periodic law describes trends seen across periods within the periodic table.
The explanation:
When the chemical elements are arranged, there is a pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties
= 3.6 mol H₂