Answer:
<em>the <u>valency of an element</u> is its combining capacity that is the number of electrons it requires to lose, gain or share in order to become neutral.</em>
[ An element can become neutral if it completes it's octet. That is if an element has 8 electrons in it'd outermost shell then it is considered neutral ]
- The valence of Magnesium is 2 because it requires to lose 2 electrons to become neutral.
- whereas, the valence of Oxygen is 2 because it needs to gain 2 electrons to become stable.
Hence they both have the same valence.
One may say that oxygen's valence is -2 while that of Magnesium is + 2. It's meaning is still the same but "-" sign indicates that oxygen will be gaining electrons in the process of becoming stable.
Stoichiometry measures these quantitative relationships, and is used to determine the amount of products/reactants that are produced/needed in a given reaction.
<span>250 ml * 1.25 g/ml * 3.74 j/g-K * 9.2 K = 10.752 kJ
Pretty much, all you need to do here is multiply all of these out to get your final answer. Not all questions are this easy, but this is certainly one of them.</span>
