**Core Concept**
The HIV virus belongs to the family Retroviridae, characterized by their unique replication mechanism involving reverse transcription of their genetic material. This genetic material is essentially a single-stranded molecule that is crucial for viral replication and transmission.

**Why the Correct Answer is Right**
The HIV virus contains a single-stranded RNA genome, which is a key feature of retroviruses. Upon entry into the host cell, the viral RNA is reverse transcribed into double-stranded DNA, using the enzyme reverse transcriptase. This double-stranded DNA is then integrated into the host cell's genome, where it can remain dormant until activated. The single-stranded RNA genome is essential for the viral replication cycle, as it serves as the template for the synthesis of new viral particles.

**Why Each Wrong Option is Incorrect**
**Option A:** Single stranded DNA - This is incorrect because HIV, like all retroviruses, contains RNA as its genetic material, not DNA.

**Option C:** Double stranded DNA - While HIV does convert its RNA genome into double-stranded DNA during the replication process, this is not the form in which the virus is initially packaged.

**Option D:** Double stranded RNA - This is incorrect because HIV contains single-stranded RNA, not double-stranded RNA.

**Clinical Pearl / High-Yield Fact**
Retroviruses like HIV rely on the enzyme reverse transcriptase to convert their RNA genomes into DNA, which can then be integrated into the host cell's genome. This unique replication mechanism is a key feature of retroviruses and is exploited by antiretroviral therapies to inhibit viral replication.

**✓ Correct Answer: B. Single stranded RNA**