Which of the following has a higher electronegativity oxygen or selenium?

Idon’t know how to solve this question

Under normal conditions, describe how increasing the temperatures effects the solubility of a typical salt

Abeaker with 2.00×102 ml of an acetic acid buffer with a ph of 5.000 is sitting on a benchtop. the total molarity of acid and conjugate base in this buffer is 0.100 m. a student adds 4.70 ml of a 0.360 m hcl solution to the beaker. how much will the ph change? the pka of acetic acid is 4.740.