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

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 .

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?

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

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

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.

What age, in Peaks of Maturation in Pediatrics, is there an accelerated frontal executive system development?  

Visual deficits are usually not present in a case involving brain injury.

At what age, in Peaks of Maturation in pediatrics, does frontal executive function mature?