Explanation: Mass is Kilogram
Weight is Newton
no, it not useless. we still learn Bohr's model in HS n dats almost 200 yr old! while there may be new models, previous one is good for explaining the basics. it is also useful to learn previous model n see how our understanding improves over time.
In order to calculate the thermal energy, first let's calculate the power, using the formula:

For a voltage V = 9 Volts and a resistance R = 50 ohms, we have:

Now, multiplying the power by the time (in seconds), we can find the energy:

In scientific notation, we have an energy of 7.3 * 10^2 J, therefore the correct option is the fourth one.
Calcium has 2 valence electrons
I do believe that the answer is D.
Hope this is right! Have a great day! :-)