INVERSION AND DIPOLE MOMENT????

1. yes giri most reaction undergoing SN₂ reaction undergo inversion(called walden or umbrella inversion). for eg C₂H₅NH₂ is not an exception too it undergo nucleophilic substitution by SN₂ and thus inverts (also notice that compound is 1⁰ so it can easily undergo SN₂

2. order is 4<3<2<1 reason
a.. as s character increses electronegativity dec due to which net dipole moment of compound due to Cl dec
thats y the order 3<2<1

b.. if a electronegative gp (like CO) is attached to C then also net dipole moment due to Cl dec
thats y the order 4<3

thats rite giri but see also that na ki agar CO most -I hai then the dipole moments of CO & Cl will cancel each other to a larger extent