Question

*The major demerit of Mendeleev's periodic table is that the element _______ could not be properly positioned.*

1️⃣ Helium
2️⃣ Hydrogen
3️⃣ Alluminium
4️⃣ Chlorine​

Answer 1

The major disadvantage of Mendeleev's periodic table is that the element Hydrogen could not be properly positioned.

Mendeleev's periodic table

• Mendeleev was the first Russian scientist who put together the elements in a systemic way based on their atomic mass as well as internal characteristics.
• However, his table had certain limitations.
• He failed in locating Hydrogen on the periodic table.
• This was because Hydrogen's characteristics resembled both, alkali metals as well as halogen.
• Hydrogen has only one electron in its outermost shell similar to other alkali metals( Na, Al)
• Also, it resembles halogens since it requires only one more electron to complete its electronic shell configuration. Eg, Fluorine, chlorine etc

The options 1) helium, 3) Aluminium, and 4) Chlorine are incorrect since they were positioned easily in the table.

(#SPJ3)

Answer 2

The correct option is : B

1. Hydrogen in entire periodic table cannot be positione.

2. It exhibits propertoes of mets and non-metals both.

3. It has 1 electron in it's outer shell which can be either donated or 1 electron can be accepted to acquire Inert Configuration. Thus, achieving stability.

4. We know that on extreme right we have non-metals while on left we have metals. So,hydrogen cannot be positioned in neither of them.

5. Hence, option B is correct.