The two ways that energy can be transferred are as heat or as work. True or False?

Answer:

Helium will be inert. Lithium is the most reactive element, followed by chlorine.

Explanation:

The elements tend to resemble the closest noble gases in terms of their electronic configuration of the last layer, that is, having eight electrons in the last layer to be stable. Then, the reactivity of an element measures the tendency to combine with others to generate the mentioned stability.

Within a period, the groups located on the left of the periodic table are more reactive than groups on the right. This is because it is easier to lose the electron of the last layer possessed by the elements located on the left than more than one electron in the rest of the elements. When we reach a certain group the trend is reversed since it will be easier to gain the missing electrons to resemble the nearest noble gas. Therefore, in a period the reactivity of metals increases the further to the left in the period (less electrons to remove). The reactivity of nonmetals increases as the period progresses since it is the case in which it is easier to acquire electrons to acquire stability, and increases to advance in a period since the less electrons they need to acquire, the more reactants they are.

Within a group, as we descend into it, the electrons of the last layer are farther from the nucleus and, therefore, it will be easier to remove them. In the case of nonmetals, it will be more difficult to take electrons. Then the reactivity of the metals increases when advancing in a group (greater tendency to lose electrons) and the reactivity of the nonmetals increases the higher in the group (greater tendency to take electrons).

Finally, you have noble or inert gases. Its inert name is due to the lack of reactivity with other elements. This is due to its electronic configuration, because its outermost layer or valence layer is always complete, without the need to share, transfer or receive electrons forming bonds. That is, its outer layer is so stable that the element tends not to react with others except in very specific cases.

Taking into account everything mentioned above, it is possible to say that helium is a noble gas, so it will be inert. Lithium is the most reactive element, followed by chlorine.

Answer : Option A) Sodium

Explanation : Sodium is the element which is most reactive tin the given options.

Sodium has the atomic number as 11, which is distributed in the atomic shells as 2-8-1.

So, it is clear that the outermost valence shell contains only one electron in sodium. To give away one electron and attain the octet state is easy for sodium. If it donates the electron it becomes a cation which is very reactive, as it gets a positive charge on itself.

Compared to the valency of the other atoms given here, Nickel has 2 valence electrons so it will be less reactive than Sodium.

Carbon has 4 valence electrons which is less than sodium and oxygen needs 2 electrons to be an octet which is also less.

Answer:

By measuring the total mass of the matter before as well as after any physical or chemical change.

Explanation:

As mentioned, according to the law of conservation of matter, no atoms can be created or destroyed when under physical or chemical change.

Naturally, all the matters have some mass associated with it.

To verify the law of conservation of matter, at first, measure the mass of matter before it underwent any physical or chemical change. Then, again, measure the mass of the matter after the physical or chemical change.

Now, observe both the mass, both must be equal. This verifies the law of conservation of matter.