Answers:
1. 2 strands. (known as polynucleotide)
2. DNA is double stranded while RNA is single stranded.
3. Hydrogen bonds.
There are four types of them;
• Adenine and Thymine are double H-Bonds.
• Guanine and Cytosine are triple H-Bonds.
Additional:
Other Differences between DNA and RNA:
•DNA contains the sugar deoxyribose, while RNA contains the sugar ribose.
• DNA is stable under alkaline conditions while RNA is unstable.
•DNA is responsible for storing and transferring genetic information while RNA directly codes for amino acids and acts as a messenger between DNA and ribosomes to make proteins.
I hope it's helpful :)