My prefix is crossed out, for ancients,
My infix is a valley, for genii,
My suffix is charged, for ever,
And my whole is a breaking point.
What am I, and why?
You are:
TENSION
My prefix is crossed out, for ancients,
In ancient Rome, the number TEN is written as an 'X', or cross.
My infix is a valley, for genii,
'Silicon Valley' is a global hub for innovation and new technologies - the playground of innovative genii, perhaps. The chemical symbol for the Periodic Table element silicon is Si.
My suffix is charged, for ever,
As found by @Amoz already, an ION is a charged particle in chemistry.
And my whole is a breaking point.
Altogether, TEN + Si + ION (with overlap) is TENSION: the state of being stretched tight (either physically or mentally) and possibly about to break...
You are an
EXECUTION!
My prefix is crossed out,
EX is "ex-ed out"
My infix is a valley,
A CUT is a synonym for valley
My suffix is charged,
This is the classic clue for ION
And my whole is a breaking point.
Together we get EXECUTION, the breaking point, or end, of one's life
How about a
decision
This is very much piggybacking on Stiv’s answer but
deci an abbreviation for ten which is Roman numeral X which is crossed out.
The valley, as identified by Stiv
si for Silicon Valley
Charged, as identified by Stiv
ion
And why?
a decision is loosely synonymous with a breaking point, more so than just tension (sorry Stiv. I feel like I’m robbing you if this is it.)