Step 1: Understand what a patent gives.
A patent under the Patents Act, 1970, gives an inventor exclusive rights to use their invention. But these rights are not absolute. We must find a true limitation on them.
Step 2: Why are there limits?
The law balances private rights with public interest. The Government may sometimes need to use an invention for public benefit, so the Act carves out special powers for the State.
Step 3: Look at the Government use provision.
Chapter XVII of the Act, and especially Section 100, allows the Government, or anyone authorised by it, to use a patented invention for the purposes of the Government even without the patentee's consent.
Step 4: Match this with the options.
Option B says the Government may use the invention for its own purposes without the patentee's consent. That is precisely what Section 100 allows. So B looks correct.
Step 5: Eliminate the wrong options.
Option A says the Government cannot use it without permission, which is the opposite of the law. Option C says the patent becomes void if the Government uses it, which is false. Option D says the patentee loses all rights once the Government uses it, which is also false, since the patent stays valid. So A, C, and D are wrong.
Step 6: Confirm the limitation.
The genuine limitation is that the State can use the invention for its own purposes without asking the patentee.
Step 7: Final answer.
\[ \boxed{\text{The Government may use the invention for its own purposes without the consent of the patentee}} \]