Answer:
7. Option 2. Atom 1 and Atom 4
8. The same number of valence electron
Explanation:
7. Determination of which symbol represent an isotope.
Isotopes are atoms having the same atomic number but different mass number due to the difference in the neutron number.
From the question given above, the following were obtained:
Z => atomic number
A => mass number
Atom >>> Isotope >>>>> Z >>>> A
1 >>>>>>> ¹⁷₇E >>>>>>>> 7 >>>> 17
2 >>>>>>> ¹⁷₈E >>>>>>> 8 >>>> 17
3 >>>>>>> ¹⁸₆E >>>>>>> 6 >>>> 18
4 >>>>>>> ¹⁸₇E >>>>>>> 7 >>>> 18
From the table above, only atom 1 and 4 has the same atomic number. Hence, atom 1 and atom 4 are isotopes.
8. To know the correct answer to the question, we shall write the electronic configuration of magnesium and calcium. This can be obtained as follow:
Mg (12) => 1s² 2s²2p⁶ 3s²
Valence electron => 2
Ca (20) => 1s² 2s²2p⁶ 3s²3p⁶ 4s²
Valence electron => 2
We can see that magnesium and calcium both have the same valence electron. Hence, they will have similar chemical properties.
