Chemistry Test 210

The correct chronological order for the discoveries of the scientists is:

B: Dobereiner, Chancourtois, Newlands, Mendeleev

• Johann Wolfgang Döbereiner (1829) - Known for his law of triads, grouping elements into sets of three based on similar properties.
• Alexandre-Émile Béguyer de Chancourtois (1862) - Developed the telluric screw, an early 3D arrangement of elements based on atomic weights.
• John Newlands (1865) - Proposed the Law of Octaves, noting periodicity in elemental properties every eight elements.
• Dmitri Mendeleev (1869) - Created the Periodic Table, arranging elements by increasing atomic weight and predicting undiscovered elements.

Electrovalent bond is formed as a result of electrostatic attraction between the positive and negative ions.

Zn, Cd, Hg do not show properties of transition elements hence they are known as non typical transition elements.

ince 'R' gives a colourless gas on reaction with dil HCl, so it contains CO₃^2- or SO₃^2- as anion (i.e., CO2 or SO₂ is evolved).

Since the gas decolourises acidified KMnO4 solution so it is SO₂ and thus the anion present is SO₃^2- i.e., the salt 'R' is Na₂SO₃ .

Elements (a), (b) and (d) belong to the same group since each one of them has two electrons in the s sub shell. In contrast, element (c) has seven electrons in the valence shell and hence does not lie in the same group in which elements (a), (b) and (d) lie.

Transition metals are generally paramagnetic since they contain unpaired electrons.

Non-metals are mainly placed in p-block elements.

In formation o f Cl₂ molecule a pair o f electrons is shared between the two chlorine atoms. Each chlorine atom contribute one electron to the shared pair.

They may or may not be diamagnetic

The elements of the second period show similar properties as the elements of the third period, which are diagonally placed to them.