Which type of rock forms as a result of cooling and crystallization?

The answer is igneous rock.

Explanation:

There are three types of rocks:

Sedimentary rocks: these are the rock which composed of sand particles , pebbles, stones , shells etc and other fragments of material. There gradual accumulation over each other in the form of layers with a span of time gets harden and take s the shape of a big rock.

For example : limestone

Metamorphic rocks: These are the rock form under the surface of the rock due to high temperature and pressure under the earth surface.

For example : marble.

Igneous rocks: These are the rocks which are formed due to cooling of hot molten rocks that is magma.Sometimes under the earth due to cooling and hardening. Some times these types of rocks are also formed on the surface of the earth, by the means of eruption magma comes to surface of the earth and due fast cooling it gets hard to form rock.

For example : obsidian.

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.