Answer:
Helium is in group 18 of the periodic table. How is helium different from the other elements in this group? = Helium atoms have 2 valence electrons, while atoms of the other elements in the group all have 8 valence electrons.
An emission spectrum will occur when = An electron releases energy and falls back to a lower energy level.
Explanation:
Answer: Options (a) and (d) are the correct answer.
Explanation:
A catalyst is the substance which helps in increasing the rate of reaction.
Activation energy is the minimum amount of energy required by reactants to start the reaction. On addition of catalyst, the path of reaction changes because the energy barrier gap reduces and hence, the activation energy also decreases.
In the absence of catalyst, we need to increase the temperature so that reaction can occur quickly.
Whereas on addition of catalyst, there is no need to increase the temperature as the catalyst itself is sufficient to increase the rate of reaction. As a result, temperature should be lowered when there is addition of catalyst in the reaction.
Thus, we can conclude that catalysts can save money by essentially lowering the activation energy and temperature required.
When carrying out experiment in the laboratory to investigate physical changes, absolute measurement is usually not needed. For instance, one can just take a little sample of sodium chloride and dissolve it in water to demonstrate physical change. But for other experiments, such as the measurement of the catalase enzyme activity in a liver tissue. Careful measurements have to be made when preparing the chemicals that will be used in the experiment.
Explanation:
It is known that heat (Q) required to change the phase of a given sample of mass m will be as follows.
........ (1)
where, 
= latent heat of fusion
Similarly, 
= mL_{v}[/tex] ....... (2)
where, 
= latent heat of vaporization
As it is known that value of latent heat of fusion of water is 334 J/g and latent heat of vaporization of water is 2260 J/g.
Hence, equating both the equations as follows.
= 
= 
= 
= 54.13 g
Hence, we can conclude that 54.13 grams of ice will melt.
A
Explanation:
The coiling up of DNA with the help of histone proteins - to what is called heterochromatic regions- is part of gene regulation. This makes genes inaccessible to RNA polymerase that makes mRNA from the genes. When the genes are exposed by DNA unwinding, these genes are transcribed and the resulting mRNAs are translated by ribosomes into proteins.
The DNA never unwinds completely, but rather does so region by region, because if it does so it would become so long that it wouldn't fit in the nucleus or cell.
