In this case, document.getElementById won't work, just as felgall said before.
But there is another way for you to get the ID of an option.
You can put anything you want in the tags of any element.
if you write <inptu type="button" id="X" VaRiAbLe="This is a variable" />, alert(document.getElementById("X").VaRiAbLe) will return "This is a variable".
With options you can't do this, but you can access an option that can have a specific id just making a loop throughout the <select> tag.
<option id="opt2">opt 2</option>
for( var i=0; i<document.getElementById("selecao").options.length; i++)
if( document.getElementById("selecao").options[i].id == 'opt2' )
It's not the fastest way, but it will work fine.
I hope this can be useful for you. =)