Answer:
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Explanation:
double blind test. the control group receives a placebo. Why is a placebo used in a double-blind test? so that the effects on people in two different groups can be compared.
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Answer:
- The standard form of a chemical element is the natural mixture of several isotopes of the same element, which is atoms with the same number of protons but different number of neutrons, while an isotope is a particular kind of atom with a definite number of neutrons.
Explanation:
A <em>chemical element</em> is a pure substance formed by atoms with the same atomic number (number of protons). This is because it is the number of protons what identifies an element.
For example: oxygen is a chemical element, so oxygen is formed by only atoms of oxygen, and the atomic number of those atoms is 8, because every oxygen atom has 8 protons.
Nevertheless, some atoms of oxygen, may have different number of neutrons. Isotopes are different kind of atoms of the same element, which only differ in the number of neutrons. So, some atoms of oxygen will have 8 neutrons, other 9 neutrons, and other 10 neutrons (those are the stable isotopes of oxygen).
That difference in neutrons, is generally accepted that, does not modifiy substantially the chemical properties of the element, but the mass number. So, the isotopes with more neutrons wil be heavier, and the isotopes with less neutrons will be lighter.
- Mass number = number of protons + number of neutrons.
In general a chemical element is formed by a mixutre of isotopes of the same element.
Same as a normal human would have. 24 ribs or 12 pairs of ribs in each side. There is no discrepancy in the number of ribs whether the human is old or young; male or female (contrary to the unpopular belief that a male has an extra pair of ribs).
The SI base unit for amount of substance is the mole. 1 mole is equal to 1 moles Calcium Chloride, or 110.984 grams.
