chemistry questions

please answer the four questions below.

 1. An element has the following natural abundances and isotopic masses: 90.92% abundance with 19.99 amu, 0.26% abundance with 20.99 amu, and 8.82% abundance with 21.99 amu. Calculate the average atomic mass of this element.

2.       2. Determine the empirical formulas for the following compounds:

 (a) acetic acid, C2H4O2

(b) citric acid, C6H8O7

(c) hydrazine, N2H4

(d) nicotine, C10H14N2

(e) butane, C4H10

3. Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each.

(a) the chalcogen with a mass number of 125

 (b) the halogen whose longest-lived isotope is radioactive

 (c) the noble gas, used in lighting, with 10 electrons and 10 neutrons

(d) the lightest alkali metal with three neutrons

4. For each of the following pairs of ions, write the symbol for the formula of the compound they will form:

(a) K+, O2-

 (b)NH4+, PO43−

(c) Al3+, O2−

(d) Na+, CO3 2−

(e) Ba2+, PO4 3−