17) the elements sodium, magnesium, and silicon
a) are isotopes of each other
b) are in the same period of elements

A period is a horizontal row and therefore these elements are all in the same period.

If you pull up an image of the periodic table, you will see that all of them are in the same row.

They are not isotopes of each other because an isotope is the same element with a different number of neutrons (example: carbon-12, carbon-13).

Hopefully I helped :)

B) are in the same period of elements.

Explanation:

The elements sodium, magnesium, and silicon

A) are isotopes of each other . NO. Isotopes are 2 or more forms of the same element, with a different number of neutrons.

B) are in the same period of elements. YES.

Let's consider the electron configuration of these elements.

₁₁Na 1s² 2s² 2p⁶ 3s¹

₁₂Mg 1s² 2s² 2p⁶ 3s²

₁₄Si 1s² 2s² 2p⁶ 3s² 3p²

Since the valence electrons are in the level 3, they all belong to the third period in the periodic table.

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !