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molybdenum-96 Z = 42 & A = 96 Z = the number of protons Z = the atomic number A = the atomic mass A = the atomic mass number Z + n0 = A or A - Z = n0

Reading the periodic table:

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Fill in the table showing Z and A in the symbol, like in the example of molybdenum given above. Since these atoms are neutral they have the same number of electrons as protons. So the overall charge for all of them is 0.

For these problems you need to know how to read the names of isotopes.
In aluminum-27 the word gives you the name of the element. The number gives you the mass of the isotope. Find the element on the periodic table. The atomic number (see key above) tells you how many protons that element has. The mass tells you the sum of protons plus neutrons for that isotope.

Name	Symbol	Z No. of p+	A - Z No. of n0	A Mass	No. of e–	Overall Charge
nitrogen-15	157N	7	8	15	7	0
oxygen-16						0
oxygen-18						0
magnesium-26						0
magnesium-24						0
phosphorous-31						0
calcium-40						0
calcium-42						0
silicon-28						0
silicon-30						0
neon-22						0

Drawing

Draw each of the atoms from the table above in a way that clearly shows the number of protons, neutrons, and electrons. Do this on a separate piece of paper. Put the electrons in circles around the nucleus:
2 in the first circle
8 in the next circle
18 in the next circle
32 in the next circle (if needed)