There are ten dL in one litre, so an ideal amount of lead in a litre of blood would be no greater than 400 micrograms (ug)
There's 1000mL in a litre, so we're looking at 0.4ug of lead or less in a millilitre. 1mol of lead atoms weighs about 207.2g, therefore there's about 2.907 × 10^21 atoms per gram, or about 1.163×10^14 atoms in 0.04ug. Therefore there should be no more than 1.2×10^14 atoms of lead per millilitre.
B. inference because she drew a conclusion based on evidence.
Because the evidence was that she heard the crashing sound, and then when she came into her room saw the broken window and baseball.
It was not an observation because she did not directly see the baseball going through the window
Fe is the element Iron, the 2+ is how many electrons is lost to make the ion, so 2 electrons are lost from the valence shell (to make a full outermost shell)