Answer:
atomic number of Be =4
electronic configuration :1s²2s²
but for Be2+ atomic number = 4-2 =2
electronic configuration : 1s²
I would think the last one about the ozone layer
Answer:
endo takes energy in and exo releases it out
Explanation:
Depression in freezing point (Δ

) =

×m×i,
where,

= cryoscopic constant =

,
m= molality of solution = 0.0085 m
i = van't Hoff factor = 2 (For

)
Thus, (Δ

) = 1.86 X 0.0085 X 2 =

Now, (Δ

) =

- T
Here, T = freezing point of solution

= freezing point of solvent =

Thus, T =

- (Δ

) = -