5F2 +2NH3 = N2f4 + 6HF
moles = mass/molar mass
mass =molar mass x mole
a) moles of Nh3 = 58.5/17 = 3.44 moles
the mole ratio of F2:NH3 = 5:2
the moles of F2 =3.44x5/2=8.6 moles
mass= 8.6 x 38 = 326.8 grams of F2
B) moles of Hf = 3.89/20 = 0.1945 moles
mole ratio NH3:Hf = 2:6
moles of NH3 = 0.1945 x2/6 = 0.0648 moles
mass =0.0648 x17 = 1.102 grams of NH3
C) moles of f2 = 217/38 =5.711 moles
mole ratio N2F6:F2 = 5:1
moles of N2F4 =5.711 x1/5 =1.142 moles
mass = 1.142 x104 = 118.77 grams of N2F4
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 
It determines the manner in which it develops bonds.... so, it affect ionization energy, electronegativity, metallic characteristic, formation of oxides etc.
#6: The living organisms in an ecosystem can be divided into three categories: producers, consumers and decomposers. They are all important parts of an ecosystem.
#7: Nature has its own recycling system: a group of organisms called decomposers. Decomposers feed on dead things: dead plant materials such as leaf litter and wood, animal carcasses, and feces. They perform a valuable service as Earth's cleanup crew
HOPE THIS HELPS
When ice cream melts from solid to liquid, the motion of the molecules increases. This is because as the phase change moves from solid to liquid to gas, entropy increases which increases the probability of the molecules to collide and move in the system. This increase may be because of the increase in temp, probable cause of the melting of icecream.
