## **Core Concept**
The question pertains to key facts about bone tumors, including their types, characteristics, and diagnostic approaches. Understanding the distinctions between primary and metastatic bone tumors, as well as specific radiological and clinical features, is crucial.

## **Why the Correct Answer is Right**
The statement that **most common malignant tumour of bone is metastases** is accurate. Metastatic bone disease is indeed more common than primary bone malignancies. **Multiple myeloma** is recognized as the most common primary malignant bone tumor, making this statement correct as well. The **Codman triangle**, which represents a radiographic sign of bone malignancy where the periosteum is lifted off the bone by a growing tumor, creating a triangle-shaped appearance, is highly suggestive of **osteosarcoma** but not exclusively specific. **CT scan** is not the most appropriate initial imaging modality for detecting skeletal metastases; **MRI** and **bone scan** are often more sensitive. **Blow out bone metastases** are indeed characteristic of **renal cell carcinoma**, which can cause highly aggressive and lytic bone lesions.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while some statements might be true, without evaluating each statement's accuracy, we cannot confirm its correctness.
- **Option B:** Similarly, this option's correctness depends on the evaluation of the statements provided in the question.
- **Option D:** This option suggests that not all statements are true, which might be incorrect based on the verification of each statement.

## **Clinical Pearl / High-Yield Fact**
A critical clinical pearl is that **multiple myeloma** is the most common primary malignant bone tumor in adults, often presenting with **lytic bone lesions** and **hypercalcemia**. Another key point is that while **Codman triangle** is highly suggestive of **osteosarcoma**, it is not pathognomonic.

## **Correct Answer:**
**Correct Answer: B.**