Cale on the How do scientists use parallax to measure the distance to nearby stars?
A Parallax increases the focal length of the lens in a telescope.
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B.
Parallax helps classify stars according to brightness and temperature.
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C. Parallax shows the apparent movement of a star seen from different positions.
D. Parallax helps identify the chemical composition of stars.
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the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.