Additional
1) particles of a pure substance that cannot be decomposed by ordinary chemical means are called what ?

Particles of a pure substance that cannot be decomposed by ordinary chemical means are called Elements .

Explanation:

Elements are the purest form of the substances that cannot be decomposed by any of the ordinary chemical means such as heating, electrolysis and reaction. Only those substances that has been formed through combination of the elements can be decomposed by the ordinary chemical means due to the presence of elements like sodium, hydrogen, carbon dioxide as well as oxygen because these things upon heating decomposes.  

b.

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.