What is the number after an elements name, representing the sum of its protons and neutrons

How can two atoms of the same chemical element be different? A. They may be different isotopes of the element. Each isotope of the same element has a different number of electrons. B. They may be different isotopes of the element.

The circles in the diagrams below represent energy levels in an atom, and the arrows show electron (blue dot) transitions from one energy level to another.

Show the reaction sequences that explain these transformations

A car driver accelerates to a speed of 35 mph and then takes her foot off the gas pedal. Even though she does not press the brake pedal at any time, she eventually rolls to a stop. Which of the following most likely causes the car to come to a stop?

The ability of a material to be pounded into thin sheets is called what

Convert 45.8g of CO2 to mol

Suppose that 0.95 g of water condenses on a 75.0 g block of iron that is initially at 22 °c. if the heat released during condensation is used only to warm the iron block, what is the final temperature (in °c) of the iron block?

How many grams of NaOH are produced with the reaction of 5.00 moles of water?

Describe the physical properties of water

Which element has the same number of valence electrons as oxygen--. a. Neon-b. Nitrogen-c. Sulfur-d. Fluorine