Step 1: Understand the section.
Section 3 of the Environment (Protection) Act, 1986 gives the Central Government wide powers to protect and improve the environment. The question asks what falls specifically under Section 3(2)(ii).
Step 2: Break down Section 3.
Section 3(2) lists several specific powers in separate sub-clauses. Each small clause covers a different action, so we must match the correct clause to the correct power.
Step 3: Identify clause (ii).
Section 3(2)(ii) empowers the Central Government to lay down standards for the quality of the environment in its various aspects. This means setting quality benchmarks for air, water, and so on.
Step 4: Match the other clauses.
Planning a nation-wide programme is under Section 3(2)(i), carrying out investigations and research is under Section 3(2)(iii), and collecting and spreading information is under another clause. So these belong elsewhere.
Step 5: Pick the right option.
Only the option about laying down standards for the quality of the environment matches Section 3(2)(ii). The other options belong to different sub-clauses.
Step 6: State the answer.
So Section 3(2)(ii) covers laying down environmental quality standards. \[ \boxed{\text{Laying down standards for the quality of the environment in its various aspects}} \]