What best describes index fossils?

Organisms that existed over a limited period

Organisms whose age is hard to detect

Fossils that are used in radioactive dating

Fossils of the most ancient organisms

Idon’t know how to solve this question

Predict the products butane (c4h10) + oxygen —>

Given the following at 25c calculate delta hf for hcn (g) at 25c. 2nh3 (g) +3o2 (g) + 2ch4 (g) > 2hcn (g) + 6h2o (g) delta h rxn= -870.8 kj. delta hf=-80.3 kj/mol for nh3 (g), -74.6 kj/mol for ch4, and -241.8 kj/mol for h2o (g)