How many identified isotopes does samarium have?

We just started a new lesson in chemistry and everyone hates it and i dont get it one bit. i hate school. h el p.balanced equationc3h8+5o2-> 3co2+4h2o1.) if you start with 14.8g of propane(c3h8) and 3.44g of oxygen, which is the limiting reactant -check my answer 2.)what mass of excess reagent is left over? 3.)what mass of carbon dioxide can be made? 4.)what mass of water is produced?

What is the result of multiplying (2.5 × 1010) × (2.0 × 10-7)? a. 5.0 × 103 b. 5.0 × 10-3 c. 5.0 × 1017 d. 5.0 × 10-17

Drive down any three characteristic of modern periodic table