Which of the following is an ionic compound ? a. gold
b. water
c. carbon monioxide
d. magnesium chloride

Among the given choices, the ionic compound is D. Magnesium Chloride (MgCl2) where magnesium has a +2 charge while chloride has a -1 charge. Ionic compounds are chemical compounds comprising of ions held together by electrostatic forces named as ionic bonding.

Initial velocity,  u = 4.9 m/sfinal velocity = v m/sinitial height,  h₁ =  245 m    final height, h₂ = 0a = -9.8  m/s²time taken = t secondss = ut + 0.5at²⇒  (h₂-h₁) = ut + 0.5at²⇒  0-245 = 4.9t + 0.5×(-9.8)×t²⇒ -245 = 4.9t - 4.9t²⇒ 4.9t² -4.9t -245 =0solving it, we get   t = 7.59sv  = u +  at = 4.9 -9.8×7.59 = 4.9 - 74.38 = -69.48 m/svelocity is  69.48 m/s downward