Due to lanthanide contraction, there is a poor shielding of 4f electrons. In this phenomenon, the inner-shell electrons shield the outer-shell electrons in a way that their nuclear charge is not affected. Due to weaker shielding, the positively charged nucleus has a greater attraction to the electrons which leads to the decreased atomic radius on increasing the atomic number. Hence corresponding elements of second and third transition series have similar atomic radii. The correct option is B and A

Due to the smallest size of Lu³⁺, the hydroxide of Lu will dissolve readily in the hot concentrated alkali.

Be does not combine with hydrogen to form hydride. Therefore, the thermal stability of the hydrides is in such a manner. For the other options, the reverse order of the given order is correct.

In aqueous solution, the covalent bond present in dimer are broken due to high hydration enthalpy of Al³⁺and Al complex and Cl^- ion is formed.

Liebig’s combustion method 

Whereas, (b) and (c) are used for estimating the percentage of nitrogen and (d) is used for estimation of halogens.

In a titration of a strong acid vs weak base, an indicator with acidic range i.e. methyl red (pH = 4.4 – 6.5) is used.

The appropriate hierarchy of (-I) effect for the following compounds: -NO₂ > -CN > -COOH > -F > -Cl > -Br > -I > -OH > -OCH₃ > -C₆H₅ > -H

cis-trans isomerism is due to restricted rotation either due to carbon-carbon double bond or due to cyclic structure. 

Geometrical isomerism: the isomers which possess the same structural formula but differ in the spatial arrangement of the groups around the double are known as geometrical isomers. 

Here, total 4 carbons and one double bond are there: therefore, butene 

And 2 methyl groups are attached on carbon: therefore, dimethyl 

Numbers are given as above so, 3,3-dimethyl butene

The compound 

4 carbons and 1 double bond are there: butene 

1 methyl group is attached on carbon and number system is given as above 

So, 3-methyl-1-butene