A law is statement about an observed concept. A theory involves the explanation of scientific concepts or principles. A hypothesis is the predicted explanation about some concepts that has to be tested in order to prove it to be right. An observation is the observing the results of a scientific experiment carried out to test an hypothesis.
Here the given statement 'A chemist mixes sodium with water and witnesses a violent reaction between the metal and water,' can be classified as an observation as it explains what the chemists observes as a result of his chemical experiment or test..
Explanation:
Mutations on DNA create genetic variation and diversity on which natural selection acts upon. Mutation can be advantageous, disadvantageous or neutral. Those mutations that confer advantage are preserved in the population while those that are DISadvantageous are weeded out. This occurs because advantageous traits that give a particular advantage to individuals in the environment, however slightest, give them an increased chance of survival and passing their genes to subsequent generations.
An example is mutation that causes sickle cell-shaped blood cells. Individuals with sickle cell blood are less likely to contract malaria. Therefore in an environment where malaria is endemic, the population will have a higher allele frequency for sickle cell alleles that populations in non-endemic areas.
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NaCl consists of a salt, which is a nonmetal (Na) and Cl, which is a metal. When a nonmetal and a metal are combined, it makes the compound ionic.