or
  1. Atomic no. (Z) = 13 and atomic mass (A) = 27
    No. of neutrons = A-Z = 27 - 13 = 14
    No. of electrons = 13 - 3 = 10

    Al atom loses 3e- to form Al+3.

  2. The permanent change in which one compound is transformed into other compound have different properties is known as chemical change.

    Two important characters are:

    a. It is irreversible change.
    b. New compound having different properties are formed.


  3. Atomic no. (Z) = 19 and Atomic mass (A) = 39
    No. of neutrons = (A - Z) = (39 - 19) = 20
    No. of electrons = Number of protons = Atomic number

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