**Core Concept**
Lignocaine (lidocaine) is a local anesthetic that can cause systemic toxicity when administered in high doses. The addition of adrenaline (epinephrine) to lignocaine decreases its systemic absorption, thereby increasing its maximum safe dose. This allows for a greater volume of lignocaine to be used for local anesthesia without causing toxicity.

**Why the Correct Answer is Right**
The maximum safe dose of lignocaine with adrenaline is 7 mg/kg, which is twice the maximum safe dose of lignocaine without adrenaline (3.5 mg/kg). The adrenaline in lignocaine-adrenaline mixture causes vasoconstriction, which reduces blood flow to the area and decreases the absorption of lignocaine into the bloodstream. This allows for a higher concentration of lignocaine to be used without causing systemic toxicity. The adrenaline also prolongs the duration of action of lignocaine by reducing its metabolism.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because there is no established maximum safe dose of lignocaine with adrenaline for this value.
**Option B:** This option is incorrect because it is less than the maximum safe dose of lignocaine with adrenaline.
**Option C:** This option is incorrect because it is more than the maximum safe dose of lignocaine with adrenaline.

**Clinical Pearl / High-Yield Fact**
When using lignocaine with adrenaline, it is essential to be aware of the maximum safe dose to avoid systemic toxicity. This is particularly important in patients with cardiovascular disease or those who are susceptible to arrhythmias. Always check the concentration of lignocaine and the presence of adrenaline in the solution before administering it.

**Correct Answer: B. 7 mg/kg.**