Question

Q8 Name the element water is made of, what are the valencies of these elements work out the chemical
formula for water?
Q9 Write the electronic configuration for the following elements and deduce their valencies.
(1)Chlorine (2) sodium
(3) Silicon
Q What are polyatomic ions? Give examples.
i.
Define atomic mass unit. ( unit of mass equal to to 1/12th of the mass of 1 atom of c 12 isotope.
State the law of conservation of mass
11.
State +
What is meant by Avagadro's constant?
Q In which one of the following cases the number of hydrogen atom is more? 2 moles off HCL or one
mole of NH3.
Q Calculate the mass of 1 mole of each one of the following:
(a) NaCl (b) CaCO3 (c) Na2O2 (d) FeSO4.7H20 (2) CH4
Q If both K and L shells of an atom are full, what is the total number of electrons in the atom?
Q An electron has 2 electrons in the M shell. What is the atomic number of the elements?
Q Which of the following pairs are isobars?
(a) 26A", 28B38 (b) 35X79, 35780​

Answer 1

Explanation:

first ans-hydrogen and oxygen

2nd ans-

,Cl=2,8,7=(-1) valency

Na=2,8,1=(+1) valency

Si=2,8,4=4(valency)