Why the number of d-block electrons of transition elements' ions has to be between 1 and 9. What prevents them from being transition when it is 0 or 10?

Acylinder is filled with 2.00 moles of nitrogen, 3.00 moles of argon and 5.00 moles of helium. if the gas mixture is at stp, what is the partial pressure of the argon

Using the periodic table, complete the table to describe each atom. type in your answers

A4.86 g piece of metal was placed in a graduated cylinder containing 15.5 ml of water. the water level rose to 17.3 ml. what is the density of the metal. i need the steps of how to solve it to so i can use a formula to work out other problems.