This is due to the similar electronic configuration (more importantly the number of valence electrons). Among the two groups given here, choice (b) Mg, Sr and Ba are alkaline earth elements (part of group IIA) in the periodic table. Other elements of this group are Be, Ca and Ra. All these elements form the alkaline earth metal group of the periodic table. All these elements have 2 valence electrons, which they can give up to attain a +2 charge as cations. They have certain common properties, including shiny and silver-white appearance.
The backbone of the DNA strand is made from alternating phosphate and sugar residues. The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings.he backbone of the DNA strand is made from alternating phosphate and sugar residues. The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings.
This is very similar to the role that DNA helicase plays in DNA replication: DNA helicase is the zipper. It unzips our DNA strands to allow space for attachment and to expose the nucleotides that are used as a template during DNA replication and transcription.