Protons and neutrons are the sub-atomic particles present in the nucleus of an atom where as electrons are present revolving round the nucleus in orbits. Electrons are negatively charged, protons are positively charged where as a neutron is a neutral species. It is the presence of electric charge that lead to the discovery of electrons (negative charge) and protons (positive charge), while it took time to discover neutral as they were electrically neutral species. Neutrons carrying no charge were not detected easily by passing electromagnetic radiations. Therefore, neutrons were the last of the three subatomic particles, to be discovered.
Explanation:
Half life is simply the amount of time it takes for half of a substance to decompose.
Options;
- Carbon-14 has a half-life of 5,730 years. A 30 gram sample will be 10 grams after 5,730 years. This is incorrect. After 5730 years, 15g of the sample ought to remain.
- Nickel-59 has a half-life of 76,000 years. A sample would go through 3 half-lives in 228,000 years. This is correct. 3 * 76000 = 228,000
- Hafnium-182 has a half-life of 9 million years. A 38 gram sample would be 4.75 grams in 27 million years. This is incorrect. Mass after 3 half lives (27/9) = 9.5 (38 / 2 / 2)
- Iron-60 has a half-life of 1.5 million years. In 6 million years a 40 gram sample would be reduced to 10 grams. This is incorrect. Mass after 4 half lives (6 / 1.5) = 2.5 gram (40 / 2 / 2 /2 / 2)
- Lead-202 has a half-life of 52,500 years. The original sample must have been 120 grams if you have a 60 gram sample after 105,000 years. This is incorrect. Original sampe = 240 gram. So after 2 half lives (105,000/52500), mass left = 60 (240 / 2 /2)
Bronze alloy and porcelain dentures
If volume remains the same while the mass of a substance increases, the density of the substance will increase.
So if the volume remains the same while the mass of a substance decreases, the density of the substance will decrease, too.
Each nitrogen molecule had 2 Nitrogen atoms.
So 2 moles of nitrogen gas molecules will have 4 moles of nitrogen atoms.Answer is 2moles
