Answer:
Q1. D) A single replacement reaction takes place because sodium is more reactive than hydrogen.
Explanation: 
Sodium metal reacts with water to givesodium hydroxide and hydrogen gas. A single replacement reaction takes place because sodium is more reactive than hydrogen.
Sodium easily lose electrons than hydrogen and get oxidized to 
and 
get reduced to give 
.
Q2. B) It is a single replacement reaction, and the cations in the two ionic compounds are different.
Explanation: 
where Sodium is a metal and 
is an ionic compound. Na being more reactive than Al, displaces it from its salt solution.
Q3. D) 
Explanation: A single replacement reaction is one in which a more reactive element displaces a less reactive element from its salt solution.Thus zinc can easily lose electrons as compared to hydrogen and result in the formation of zinc sulfate and hydrogen.
Q4. False
no reaction
Explanation: As zinc lies lower in reactivity series, it is less reactive than calcium. It will not be able to displace calcium from its salt and hence no reaction occur. Thus the given statement is false.
Q5. False
Explanation: A double displacement reaction is one in which exchange of ions take place. Thus an element replaces another element and not same element.
A single replacement reaction is one in which a more reactive element displaces a less reactive element from its salt solution. Thus one element should be different from another element.
Q6. A)
, because K retains the same charge throughout the reaction
Explanation: A balanced chemical reaction is one in which the number of atoms on both sides of a chemical equation are same. Also K has an oxidation state or charge of +1 in 
as well as 
A) Answer is: physical separation, because there is no reaction and new substance is not synthesise.
B) Chemical separation, old bonds are broken and new ones are formed.
Chemical reaction: 2H₂O → 2H₂ + O₂.
C) Mixtures, because there are no chemical bonds between substances in the mixture.
D) Compounds, because chemical bonds betwwen elements in the compounds must be broken.
Sodium - metallic bonding
Oxygen - covalent bonding
Sodium chloride - ionic bonding
Magnesium oxide - ionic bonding
Nitrogen fluoride - covalent bonding
Aluminium - metallic bonding
Calcium hydroxide - ionic bonding
Silicon fluoride - covalent bonding (not 100% sure on this one)
Chlorine - covalent bonding
Potassium oxide - ionic bonding
The correct answer is A. cloud of gases that forms around the nucleus of a comet is called a coma. The coma is a dusty, fuzzy cloud around the nucleus of a comet. Other parts of a comet are the nucleus and the tail.
Answer:
C. All electron carriers are mobile and hydrophobic
Explanation:
Hello,
In this case, it is widely known that the electron carriers move inside the inner mitochondrial membrane and consequently move electrons from one to another. In such a way, they are mobile, therefore they are largely hydrophobic as long as they are inside the membrane.
For instance, the cytochrome c is a water-soluble protein in a large range, therefore, the answer is: C. All electron carriers are mobile and hydrophobic.
Best regards.
