The Ozone layers, i think
<h3>Explanation</h3>
Astatine has atomic number 85. "217" is the mass number of this isotope of At.
The mass number of an atom decreases by 4 as it undergoes alpha decay. Its atomic number decreases by 2. It emits an <em>alpha particle</em>, which is a helium-4 nucleus, in this process. The alpha particle has mass number 4 and atomic number 2.
The <em>daughter</em> nucleus has mass number 217 - 4 = 213 and atomic number 85 - 2 = 83. The atomic number of 83 corresponds to bismuth. Therefore the daughter nucleus is an atom of bismuth-213.
By convention, write the mass number A on the top-left corner of an element. Write its atomic number Z on the bottom-left corner. Note that A is always greater than Z for an isotope.
76.5 g I did sig figs for you:)
The answer is (4) heptane. Saturated hydrocarbon means that there is no double bonds between the carbon atoms. For propene and butene, there is double bond. For ethyne, there is triple bond.