Answer:
Something like table salt (NaCl) is a compound because it is made from more than one kind of element (sodium and chlorine), but it is not a molecule because the bond that holds NaCl together is an ionic bond. If you like, you can say that sodium chloride is an ionic compound.
Explanation:
To answer this question, you need to know the concept of half-life, which is how a radioactive material decreases in mass over time.
The half life of U-235 is 703.8 million years. The first part of this problem is to find the scale factor. To do this, divide the time that has past by the half life, like this:

Now, take this scale factor and multiply it by the current mass, like this:

This number is what you add to the current mass to get the original mass. That is because the scale factor showed us that it was just over one half life. Since after one half life, the mass is cut in half, and this is over one half life, when we add to the original it will be a little over double. This equation illustrates the final addition:

I hope this helped you. Fell free to ask any further questions.
Answer:
Aluminum is ideal for aircraft manufacture because it's lightweight and strong. Aluminum is roughly a third the weight of steel, allowing an aircraft to carry more weight and or become more fuel efficient. Furthermore, aluminum's high resistance to corrosion ensures the safety of the aircraft and its passengers.
Explanation: