Final answer:
The SJA's primary responsibility in legal assistance missions is to offer legal guidance and support to military personnel and their families on a range of legal issues.
Step-by-step explanation:
The primary responsibility of the SJA (Staff Judge Advocate) or designated Chief in the Legal Assistance mission is C) Offering legal guidance and support. This includes providing legal advice to military members, retirees, and their families on a variety of issues such as estate planning, family law, and civilian litigation, among others. The SJA and their legal team work to safeguard the legal rights of personnel within their jurisdiction and assist with navigating the complexities of military and civilian law.