Hi I have following queries
Q1 - Arrange in the order of increasing ionic radii in water and their mobility Be2+, Mg2+, ca2+, Sr2+
Q2 - Why crystalline sodium peroxide is highly hygroscopic in nature
Q3 - What is chleating effect
Q4- Which one has the highest and lowest melting point and why - Nacl, kcl, Rbcl, CsCl
Q5 - Why is anhydrous HCL predominantly covalent in gaseous state but is ionic in aqueous state
Q6 - Which of the following is incorrect
       a) In CF2=C=CF2 molecule of all four flourine atoms are not in the same plane
        b) Ka2 of fumaric acid is more than Ka2 of maleic acid due to intramolecular hydrogen bonding in maleic acid
         c) The O-O bond length in O2[AsF4] is longer than Ko2
          d) The bond angle order in -S-halogen is OSF2 <OSCl2 < OSBr2
Q7 - Why crystals of hydrated calcium sulphate are soft and easily cleaved where as anhydrous calcium sulphate are very difficult to cleave
Q8 - CO Forms Weak bonds to lewis acid such as BF3. In contrast CO forms strong bonds to transition metals. Explain

Your question is
Q1 - Arrange in the order of increasing ionic radii in water and their mobility Be2+, Mg2+, Ca2+, Sr2+

First you arrange them in increasing order of size which you know increases as we move down the group for the above series.
Now remember smaller cations are more strongly hydrated then bigger one because of more effective nuclear charge and hence more attraction with water.
Hydration radii of the smaller cation will be bigger and mass will also be more so mobility is less.
I am sure now you can figure out the answer.Please post the answer of this question as a reply.
Check below information of Alkali ions series.

Q2 - Why crystalline sodium peroxide is highly hygroscopic in nature?
N2O2 reacts with water when it comes in contact and forms NaOH and H2O2.NaOH is highly hygroscopic in nature.
Na2O2 +2 H2O -----> 2NaOH + H2O2

Q3 - What is chelating effect?
Chelating effect is stabilizing of a complex due to ring formation around the central metal ion.
Metals ions can accept electrons from ligands and stabilizes their postive changes by making complexes with lignads.However if the ligand can form a ring around the central metal ion then it becomes more stable.

Q4- Which one has the highest and lowest melting point and why - NaCl, KCl, RbCl, CsCl?
All these are ionic compounds and form lattice.
Lattice enthalpy is the energy required to break this lattice and separate ions which is also happening when we are melting these solids.
So stronger the lattice ,higher is the melting point.
Let us compare lattice enthalpy which depends on coulombic forces of attraction.
E = K q1.q2/r^2
hence it is directly proportional to charges and inversely proportional to ionic radii.It means higher charges and smaller sized ions are going to form more stronger lattice.
In our question,anion is same with same charge ...we can ignore it as it has the same effect in all of them
Now let us compare cations ...size increases as you go from Na+ to Cs+  but charges remain same on all actions as +1.
Now I am sure you can work out the answer.
Please post your answer so that I can check it.

Q5 - Why is anhydrous HCl predominantly covalent in gaseous state but is ionic in aqueous state?
H forms a covalent bond  by sharing one electron with Cl atom.So in the gaseous state it is a polar covalent compound due to difference in the electronegativity of H and Cl.
However in the presence of water .H2O acts like a base due its lone pairs on the Oxygen atom which accepts H+ from HCl molecule.This results in complete ionization of HCl molecule .

HCl + H2O -----> H3O+  + Cl-

Q6 - Which of the following is incorrect
       a) In CF2=C=CF2 molecule of all four flourine atoms are not in the same plane.
central C carbon atom is sp hybridized and uses its px and py  orbitals for making pi bonds with other carbon atoms.These p orbitals are at 90 degree with each other .Hence other two carbon atoms which are sp2 hybridized have trigonal shape at 90 degree with each other.This makes flourine atoms out of plane from each other.

) Ka2 of fumaric acid is more than Ka2 of maleic acid due to intramolecular hydrogen bonding in maleic acid

Fumaric acid is trans -dicarboxylic acid and both COOH groups are in different planes so can not undergo intra molecular H - bonding due to lack of proximity.However in Maleic acid ,both -COOH groups are in the same planes as they are on the same side of the doubly bonded carbon and hence after removal of first H it can undergo strong intramolecular H- bonging with H of other COOH group.Hence removal of second H as H+ is difficult in Maleic acid and this makes its K2 higher.

 c) The O-O bond length in O2[AsF4] is longer than Ko2
In case O2[AsF4]  it is O2+ and in KO2 it is O2-
Now from MOT
we need to work out the bond order and then bond length
O2+  electron is removed from anti bonding orbitals and hence bond order is more.
In O2- electron is added in antibonding orbital and hence Bond order is less and bond length is more.Make MOT of O2 (neutral) and then check if you remove electron and if you add electron ...how bond order is affected.

Q6 - Which of the following is incorrect
   The bond angle order in -S-halogen is OSF2 <OSCl2 < OSBr2
As the size of the atoms increases
F<Cl<Br<I
size of the orbitals holding bond pair/lone pairs on halogen  also increases and they come closer to lone pair of S /halogens and hence more repulsion .Maximum repulsion is due to LP -LP which makes these atoms to move away and hence bond angle increases.

Be2+<Mg2+<Ca2+<Sr2+

Q4.all charges same therefore order only depends on r . NaCL>KCl>RbCl>CsCl

Dear Uma maam
in Q6 part 2 what does K2 mean

Maam,
looks like these questions were missed
Q7 - Why crystals of hydrated calcium sulphate are soft and easily cleaved where as anhydrous calcium sulphate are very difficult to cleave
Q8 - CO Forms Weak bonds to lewis acid such as BF3. In contrast CO forms strong bonds to transition metals. Explain
And thanks a lot for all the other answers

In Q6 It is Ka2 (acid dissociation constant ) this you will do in detail when you will do acids and bases.

Q7 - Why crystals of hydrated calcium sulphate are soft and easily cleaved where as anhydrous calcium sulphate are very difficult to cleave?
A hydrated salt has water as the part of the crystalline structure .Water is interacting with H bonding with the ions of the crystal and creating more gaps also.H - bonding is weak IMF as compare to ionic attractions in anhydrous CaSO4 (without water).

Q8 - CO Forms Weak bonds to lewis acid such as BF3. In contrast CO forms strong bonds to transition metals. Explain.
If we compare acidity of BF3 with Transition metal cation ...transition metal cation is more acidic(tendency to gain electrons) due to high positive  charge on it and small size.
In case of BF3 ...empty 2p orbital is overlapping with filled 2p orbital of the fluorine atom and hence reducing the electron accepting tendency of BF3.