A radioactive substance has a half-life of 10,000 years. In 20,000 years, how much (%) of the original substance would remain? b. In 30,000 years? c. In 60,000 years?

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.