Look closely at the valence electrons in all eight columns of your table from part C. Which element's location does not match the pattern shown in the table?
o helium (He)
o hydrogen (H)
sodium (Na)
O argon (Ar)

they are both synthetic elements

explanation:

d

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

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a

може ли да зареждате повече информация, моля