Question

1. an atom contains 20 protons, 20 neutrons, and 20 electrons. this element is in group

a) 1 c) 4
b) 2 d) 18

1. how many valence electrons does an element located in group 14 of the periodic table have?

b) 1 b) 2 c) 3 d) 4

1. which list includes elements with the most similar chemical properties?

a) br, ga, hg c) o, s, se
b) cr,pb, xe d) n, o, f

1. which element is a metalloid?

a) al b) as c) ar d) au

Explanation:

• Question 2:
• The number of protons in an atom is equal to its atomic number. So, the atomic number of this element is \(20\).
• The element with atomic number \(20\) is calcium (\(Ca\)).
• Calcium has \(2\) valence electrons (\(4s^{2}\)) and is in group \(2\) of the periodic table.
• Question 4:
• In the periodic table, for main - group elements (groups 1 - 2 and 13 - 18), the number of valence electrons is equal to the group number minus \(10\) (for groups 13 - 18).
• For group \(14\), the number of valence electrons \(=14 - 10=4\).
• Question 6:
• Elements in the same group have similar chemical properties.
• \(O\) (oxygen), \(S\) (sulfur), and \(Se\) (selenium) are all in group \(16\).
• \(Br\) (bromine) is in group \(17\), \(Ga\) (gallium) is in group \(13\), \(Hg\) (mercury) is in group \(12\). \(Cr\) (chromium) is in group \(6\), \(Pb\) (lead) is in group \(14\), \(Xe\) (xenon) is in group \(18\). \(N\) (nitrogen) is in group \(15\), \(O\) is in group \(16\), \(F\) (fluorine) is in group \(17\).
• Question 8:
• Metalloids have properties intermediate between metals and non - metals.
• \(Al\) (aluminum) is a metal, \(Ar\) (argon) is a non - metal (noble gas), \(Au\) (gold) is a metal. \(As\) (arsenic) is a metalloid.

Answer:

• Question 2: B. \(2\)
• Question 4: D. \(4\)
• Question 6: C. \(O, S, Se\)
• Question 8: B. \(As\)