Step 1: Frame the scenario. Death of a woman within 7 years of marriage under suspicious circumstances, with dowry demand, is a dowry death. The question asks which section lets a magistrate order the autopsy.
Step 2: Section 176 CrPC empowers a magistrate (Executive or Judicial) to hold an inquiry into the cause of death and to direct the exhumation and post-mortem examination, including in cases of suspicious or custodial death. For a woman dying within 7 years of marriage in suspicious circumstances, magisterial inquiry under Section 176 is mandatory. So option B is correct.
Step 3: Option A is wrong. Section 174 CrPC deals with the police inquiry into unnatural or suspicious death; the investigating officer conducts inquest and sends the body for post-mortem. It is a police power, not the magistrate's authorisation of autopsy in this setting.
Step 4: Option C is wrong. Section 304 IPC is a punishment section (culpable homicide not amounting to murder; 304B is dowry death). It defines the offence and penalty, not the authority to order an autopsy.
Step 5: Option D is wrong. Section 302 IPC is the punishment for murder. Again it is a penal provision, not a section that authorises a post-mortem.
Conclusion: The magisterial power to inquire and order autopsy here is Section 176 CrPC. Answer: option B.