Answer:
It was the last element first discovered in nature, rather than by synthesis. Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays
<h2> The correct option is (a).</h2>
Explanation:
- There is no change of state in pouring water into a vacuum insulated bottle as the vacuum created inside the bottle only reduces the time limit for the transfer of heat by conduction and convection.
- It helps the content filled in the bottle to be hot and cool for a longer time.
Hence, option (a) is correct.
Rest of the options (b), (c), (d), (e) is not correct because of the following reasons:
- In the sublimation of dry ice, the dry ice (solid-state) is changed to the vapour form.
- In the freezing of water, the liquid state is changed to solid-state.
- During the vaporization of alcohol, the liquid state is changed to the vapour form.
- During the melting of ice, the solid-state is changed to the liquid state.
a) A combound which contains only Carbon and Hydrogen. There are covalent bonds between atoms. Hydrogen form one single bond and Carbon forms four covalent bonds. Carbon bonds can be single, double or triple bonds.
All hydrocarbons are organic compounds, but organic compound can include atoms of other elements.
b) Alkyne has a covalent triple bond between two carbon atoms. Simplest alkyne is ethyne HCCH.
b) Alkane contains only Carbon and Hydrogen and there are single bonds
between atoms. Simplest alkane is methane CH4.
c) An alkene has one double bond between Carbon atoms. Simplest
alkene is ethene H2C=CH2.
