Achemical reaction between iron atoms and oxygen molecules can only occur if

a) the particles are heated
b) the atmospheric pressure decreases
c) there is a catalyst present
d) there are effective collisions between the particle

explain why the other choices are not necessary for the reaction to take place

The answer is D) There are effective collisions between the particle[s]. Collisions between particles is what happens during a chemical reaction (in this case, the oxygen and iron particles collide).

Choice A (the particles are heated) is incorrect because heating particles will make the reaction faster. However, there must be a reaction there in the first place.

Choice B (the atmospheric pressure decreases) is incorrect because decreasing pressure will increase volume, which does not have anything to do with the speed of the reaction. Assuming you have learned about equilibrium in a chemical system/equation, you will know that changing the pressure will make the equation shift to the side with less moles of elements. However, the number of moles is not specified.

Choice C (there is a catalyst present) is incorrect because a catalyst is something that speeds up a reaction. Similarly to choice A, there is no reaction to begin with.

Hope this helps. :)

Choice number two: this element is malleable and ductile.

Explanation:

A modern periodic table can be split into three sections:

(from left to right)

Metals,Metalloids, andNonmetals.

Based on the descriptions, section A likely refers to the metals. Section B likely refers to metalloids. Section C likely refers to nonmetals.

Metals are malleable and ductile. They are good conductors of electricity.

The reason is that in a metal, the valence electrons do not belong to some specific atom. Rather, the metal cations share these electrons. The electrons are free to move around the metal and conduct electricity.

Ionic compounds like table salt are brittle. The reason is that when an ionic compound is deshaped, ions of the same charge come directly into contact with each other. That creates repulsion and cracks the crystal. In contrast, the metal cations in a metal won't come into contact with each other. Electrons would rapidly fill the gap between these cations, so the metal won't crack. That's why unlike ionic compounds, metals are malleable and ductile.

The melting points of metals can vary significantly. Indeed, the mercury (, a metal) is a liquid at room temperature. In contrast, tungsten (, also a metal) won't melt until it is heated to over .