An ore sample is found to contain 10.500000 g of cobalt and 87.3 g waste rock (gangue). What is the percent by mass of cobalt in the ore?

Explanation:

Hello!

In this case, since this is a mixture composed by cobalt and waste rock, we can compute the percent by mass of cobalt as shown below:

Thus, we plug in to obtain:

Best regards!

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

i think it's c. i'm not sure but i think so.