The correct answer is option B, which includes all the main demerits of Mendeleev's periodic table. Let's discuss each demerit in detail:

(i) Hydrogen has been placed in group I though it resembled to group VII as well:
- Mendeleev placed hydrogen in group I of his periodic table because it shared similar properties with alkali metals such as lithium, sodium, and potassium.
- However, hydrogen also shares some similarities with halogens in terms of electron configuration and bonding characteristics.
- Therefore, the position of hydrogen in the periodic table was not justified, as it could have been placed in either group I or group VII.

(ii) Positions of some elements were not justified:
- Mendeleev's periodic table was primarily based on the atomic mass of elements, and he arranged the elements in increasing order of atomic mass.
- However, in some cases, the positions of elements did not align with their observed properties.
- For example, iodine (atomic mass 126.9) was placed before tellurium (atomic mass 127.6), even though their properties indicated that tellurium should come before iodine.
- This discrepancy was due to the limitations of using atomic mass as the sole basis for arranging elements.

(iii) Isotopes were not given separate places:
- Isotopes are atoms of the same element with different numbers of neutrons.
- Mendeleev's periodic table did not account for isotopes and considered each element as a single entity with a specific atomic mass.
- This led to the omission of isotopes from the table, which was a significant drawback.
- Isotopes have different physical and chemical properties, and their inclusion in the periodic table would have provided a more accurate representation of elements.

(iv) Lanthanides and actinides were not included in the table:
- Mendeleev's periodic table did not include the lanthanides (rare earth elements) and actinides (radioactive elements from atomic number 90 to 103).
- At that time, these elements were not well-studied and their properties were not fully understood.
- Therefore, Mendeleev did not include them in his periodic table.
- However, the exclusion of lanthanides and actinides was a limitation because these elements have unique properties and should have been given separate positions in the table.

In conclusion, Mendeleev's periodic table had several demerits including the unjustified placement of hydrogen, positions of some elements, the absence of isotopes, and the exclusion of lanthanides and actinides. These demerits were addressed in subsequent developments of the periodic table, such as the modern periodic table based on atomic number and the inclusion of isotopes and the lanthanides/actinides.