It is often possible to change a hydrate into an anhydrous compound by heating it to drive off the water (dehydration). A 43.19 gram sample of a hydrate of MgBr2 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 27.21 grams of the anhydrous compound remained. What is the formula of the hydrate?

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Explanation:

Let denote the number of formula units for every formula unit. The formula of the hydrate would be .

Look up the relative atomic mass of each element on a modern periodic table:

Formula mass:

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The anhydrous compound would be . There was of this compound. Calculate the number of moles of formula units in that much of this compound:

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During heating, of water escaped from the hydrate. Calculate the number of formula units in that of :

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In other words, approximately of formula units (and hence the same number of moles of formula units) contain approximately of formula units. Calculate the ratio between the two:

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Hence, the formula of the hydrate would be .

it is b that is the answer.

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.