Answer:
2. Tin (Sn)
5. Calcium (Ca)
6. Nitrogen (N)
9. Bromine (Br)
12. Carbon (C)
13. Oxygen (O)
15. Chlorine (Cl)
17. Manganese (Mn)
20. Fluorine (F)
21. Francium (Fr)
23. Potassium (K)
25. Helium (He)
Explanation:
2. Tin (Sn)-- If you go down the period table to the fifth row (period) and to the 14th column where the Carbon family is, you will find Sn which is Tin.
5. Calcium (Ca)-- Most people know that Calcium is found in bones, but to confirm, round the atomic mass to a whole number and subtract the atomic number from it to find the number of neutrons. In this instance, the atomic mass for Ca is 40.078, which is rounded to 40. 40-20 (the atomic number) = 20, which is how many neutrons this has. Since the question was asking for the element that has 20 Neutrons, it would be Calcium.
6. Nitrogen (N)-- The 15th group (15th column) starts with Nitrogen and goes down. Since Nitrogen is a nonmetal and Phosphorus isn't usually found in its gaseous form, the element would be Nitrogen.
9. Bromine (Br)--The only liquid elements at standard temperature and pressure would be Bromine and Mercury. But, halide is a halogen atom that has negative charge. While Bromine has negative charge, Mercury has positive charge. So this element is Bromine.
12. Carbon (C)-- The atomic mass unit, otherwise known as AMU, is a unit for expressing masses of atoms, molecules, or subatomic particles. And one atomic mass unit is equal to 1/12 the mass of a single atom of carbon-12.
13. Oxygen (O)-- Since the number of protons in an element are the same as the atomic number, this should be simple to find. Going onto the periodic table, find the element with atomic number "8" and there will only be Oxygen. It is easy to find as the periodic table is ordered by increasing atomic number. Confirm the 8 neutrons by subtracting the atomic number "8" from the rounded atomic mass. In this case, the atomic mass is 15.999, rounded to 16. 16-8 is 8. The question asks for 8 protons and 8 neutrons, so Oxygen is the answer.
15. Chlorine (Cl)-- Go onto the periodic table and search for the element with the atomic mass of "35.45." You will see that the element Chlorine (Cl) has the atomic mass of 35.45 or 35.453.
17. Manganese (Mn)-- The number of electrons is the same as the number of protons. And, the number of protons is the same as the atomic number. So find atomic number 25 on the periodic table and you will find Manganese (Mn).
20. Fluorine (F)-- Fluorine has an atomic mass of 18.998, which rounds to 19. 19-9 (atomic number) is 10, which is the number of neutrons in the element. The question asks for a halogen with 10 neutrons, so it is Fluorine. [i am very sorry i don't know how to explain the halogen part im kinda doodoo on that part]
21. Francium (Fr)-- Alkali metals are the most left column of the period table, excluding Hydrogen (H). And the largest atom isn't on the right side of the periodic table; the atom will actually get smaller as you go right on the periodic table. So, the larger atoms are on the left and down part of the periodic table. So you're on the alkali metals. The larger atoms are downwards, so go all the way down and the last element on the bottom left corner would be Fr, or Francium.
23. Potassium (K)-- The banana part really gives this away, but the "period 4, group 1" also does. You go down to the 4th period (4th row) and group one, which would be the first column from the left. The K symbol is Potassium.
25. Helium (He)-- Okay I'm very sorry about this one, but I'm really not sure if this is the answer. I did learn about Rutherford but I'm not sure what element could be linked to him (maybe I wasn't paying attention in class.) BUT, Helium = Helios (God of the Sun?) And the question asked about what element was named after the sun as well so this was the best answer I could get. Sorry!
Hope this Helped!