#8- please help i suck at this, ill mark brainliest

A.  Synthesis

B.  Combustion

C.  Single-replacement

D.  Decomposition

Explanation:

A:  Synthesis.  Two reactants are combined to form, or synthesize, one product.

B:  Combustion.  This is the general reaction for combustion.  When something combusts, oxygen must be present.  Carbon dioxide and water must also be produced.

C:  Single-replacement. The oxygen from Fe₂O₃ is moved to K to form K₂O.  Only one thing is being moved, or replaced.

D:  Decomposition.  You have one compound that breaks into, or decomposes, into two products.

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.