(263.1 years) x (half-life / 87.7 years) = 3 half-lifes
In 3 half-lifes, (1/2 x 1/2 x 1/2) = 1/8 of the atoms in a sample remain unchanged.
That's 12.5% that remain unchanged.
The other 87.5% of the atoms in the sample have decayed, and changed to either other isotopes of plutonium or into atoms of other elements.
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</span><span>a. inverted and larger than the object.</span><span>
A mirror is used to see your own reflection. Earlier in the days, people would use a still water to see their reflection. It is basically used for grooming. Spherical mirrors have been used by earlier mathematicians and physicist to conduct experiments related to geometry. </span>
Elements with 7 valence electrons are extremely reactive, while elements with 8 valence electrons practically don't react at all.
This is caused by the fact that all molecules want to have 8 valence electrons; that's just the scientific fact. So, if an element already has 8 valence electrons, it doesn't need to react with anything. If the element only has 7 valence electrons, however, it really wants to react with something with 1 valence electron to get to that special number 8.
See attached
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Of these options the one which best answers the question is 'Use whatever professionals claim to use.'
It is not that professional recommendations should not be consired or valued. The reason you should not just use whatever professionals claim to use is that their needs, as professionals, may be very different from your own. In order to know whether your own needs will be met you need to know what those needs are and whether the product meets those needs. All of the other options given would help you to figure this out, but the testimony of professionals would not.