Which plane is the only horizontal plane?

Consider neutral atom which has 30 protons and 34 neutrons. The atomic number of the element is . The mass number for this atom is . The number of electron is . The symbol of element is , and its name is .

Atoms of different elements have always different number of in their nuclei.

The atomic mass of an element is equal to ________.

The smallest particle of an element that retains the characteristics of the element is a(n) .

The symbol of noble gas in the fifth period in Periodic table is

Nitrogen has two stable isotopes: N-14 and N-15. Atomic mass of nitrogen is 14.007 amu. How many neutrons are in nucleus of more abundant isotope of nitrogen?

Imaginary element has two naturally occurring isotopes. One of them has atomic mass of 60. amu and abundance 60%, and other one has atomic mass of 65. amu and abundance 40%. What is atomic mass of this imaginary element? Show your calculations.

Which of the following properties describes a solid? Check all.

AHT is formerly known as ___________. (1-3 WORDS)