You cannot convert to "standard form" without specifying a number of significant digits.
The number as written is "four hundred twenty-three billion, ninety million, seven hundred and nine thousand."
Four hundred twenty-three billion, ninety million, seven hundred nine thousand.
It is already written in standard form/notation.
365,000
The number 423,090,709,000 is "four hundred twenty-three billion, ninety million, seven hundred nine thousand."
423,090,709,000 in word form is: four hundred twenty-three billion ninety million seven hundred nine thousand.
423,090,709,000 = four hundred twenty-three billion, ninety million, seven hundred nine thousand.
423,090,709,000 = four hundred twenty-three billion, ninety million, seven hundred nine thousand.
four hundred twenty-three billion, ninety million, seven hundred nine thousand.
Four hundred twenty-three billion, ninety million, seven hundred nine thousand.
Four hundred twenty-three billion, ninety million, seven hundred nine thousand.
423,090,709,000 = four hundred twenty-three billion, ninety million, seven hundred nine thousand.
The plural of city follows the standard "-y to -ies" form, as "cities".