To solve this question, we need to correctly match each environmental disaster in List I with the appropriate phrase from List II. Let's go through each item step-by-step:

1. Bhopal gas tragedy is associated with Methyl Isocyanide. This disaster occurred in December 1984 in Bhopal, India, due to the leakage of methyl isocyanate gas from a pesticide plant. Thus, the correct match for (a) is (iv).
2. Chernobyl disaster is associated with a Nuclear accident. This tragic event occurred in April 1986 in Chernobyl, Ukraine, when a nuclear reactor exploded due to a power outage experiment gone wrong. Hence, (b) matches with (iii).
3. Love Canal tragedy involves the Dumping of Hazardous substances. This incident took place in the late 1970s in Love Canal, New York, USA, where hazardous waste was disposed of improperly, leading to health and environmental issues. Therefore, (c) pairs with (i).
4. Los Angeles smog is associated with Peroxyacetyl Nitrates (PAN). The smog, particularly noted in the 1940s and 1950s, was largely caused by the photochemical reactions involving vehicle emissions, leading to the formation of PAN. Consequently, (d) matches with (ii).

Based on this analysis, the correct matching is:

• (a)-(iv),
• (b)-(iii),
• (c)-(i),
• (d)-(ii)

This corresponds to the provided option (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii).