The nucleus of all living cells contain macromolecular species called chromosomes made up of proteins and another type of biomolecules called nucleic acids. The chromosomes are responsible for transmission of inherent characters called heredity. Nucleic acids are mainly two types: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). Nucleic acids are long chain polymers of nucleotides, so they are also known as polynucleotides. A nucleotide is composed of a base, a C₅-carbohydrate and phosphate group (orthophosphate, pyrophosphate or triphosphate), which are bonded in the sequence base–carbohydrate–phosphate. The carbohydrate molecule in DNA is \(\beta\)-D-2-deoxyribose, whereas in RNA it is \(\beta\)-D-ribose. The nucleotide act as a energy carrier and a cofactor or coenzyme for a redox enzymes. The removal of phosphate moiety from a nucleotide produces nucleoside. The N-glycoside of purine or pyrimidine bases with pentose sugars are known as nucleosides. DNA contains four bases, viz. two purine bases adenine and guanine and two pyrimidine bases cystosine and thyamine. RNA also contains four bases: the same two purine bases adenine and guanine and two pyrimidine bases cystosine and uracil (in the place of thyamine). In nucleic acids the nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar. The primary structure of nucleic acid gives the information regarding the sequence of nucleotides in the chain. The secondary structure of DNA shows that two nucleotide chains running in opposite directions and giving a right handed helix in which the two strands are held together by hydrogen bonds at definite distances.

In the secondary structure of RNA, helices are present which are only single-stranded. RNA molecules are three types: (i) messenger RNA (m–RNA) (ii) ribosomal RNA (r–RNA) and (iii) transfer RNA (t–RNA). These perform different functions. The tertiary structure gives the information of the orientation of the planar aromatic rings of the bases causing the DNA double helix to twist about the same axis. Due to twisting, a large number of hydrogen bonds are formed. The double helix of DNA is the store house of the hereditary information of the organism. The process of synthesis of RNA involving direct copying of one DNA molecule from another DNA molecule is known as replication. The process of synthesis of RNA in which a single strand DNA can act as a template is called transcription. The proteins are synthesized by various RNA molecules in the cell but the message for the synthesis of particular protein is present in DNA. This process is known as translation. In molecular biology, transcription is used as a synonym for RNA synthesis and translation is a synonym for protein synthesis. Translation is unidirectional but transcription can sometimes be reversed, i.e., RNA is copied into DNA and is known as reverse transcription.

The molecule of RNA is

smaller than DNA

The correct answer is option 1. smaller than DNA. 

In terms of size, RNA molecules are generally smaller than DNA molecules. RNA is typically a single-stranded molecule, while DNA is double-stranded. This structural difference contributes to the variation in size between RNA and DNA.

The size of RNA molecules can vary depending on the specific type of RNA and its function. For example, transfer RNA (tRNA) is typically around 70-90 nucleotides long, while messenger RNA (mRNA) can range in size from hundreds to thousands of nucleotides.

In contrast, DNA molecules are typically longer due to their double-stranded nature. The DNA molecule consists of two complementary strands that are formed by hydrogen bonding between the base pairs adenine (A) with thymine (T) and cytosine (C) with guanine (G).

Therefore, the correct answer is (1) smaller than DNA.