Which if the following elements has atoms with the least amount of valence electrons 1.k 2.ca 3.o 4.mg 5.c

Potassium (K) only has one valence electron. infact, all of the elements in the first column of the periodic table have only one valence electron.  

Idon't see the pic?

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts