Which compound has the lowest pka? (ch3ch2o2c)2ch2 ch3ch2o2cch2cho ch3ch2coch2cho phcoch2coch3 (nc)2ch2?

Aldehydes having the lowest pKa value around 17 and thus the other carbonyl have higher pKa than aldehyde.

Now, two aldehyde are present in given sereis such as

ch3ch2o2cch2cho and ch3ch2coch2cho

ch3ch2coch2cho is more acidic or having low pKa than ch3ch2o2cch2cho due to the presence of carbonyl at alpha position of aldehyde and rasonance will take place in ch3ch2coch2cho which result in release of proton readilly.

Hence, ch3ch2coch2cho having low pKa value of all and thus is highly acidic of all.

no, i was listening to water by schoolboy q while and i saw this question

explenation:

water isn't wet. wetness is a description of our experience of water; what happens to us when we come into contact with water in such a way that it impinges on our state of being. we, or our possessions, 'get wet'. a less impinging sense experience of water is that it is cold or warm, while visual experience tells us that it is green or blue or muddy or fast-flowing. we learn by experience that a sensation of wetness is associated with water: 'there must be a leak/i must have sat in something.'

"hydrogen bonding is the attraction of h atoms in the water molecule (slight + charge) to o atoms in a neighboring water molecule (slight - charge); it is a weak interatomic force. but it is still strong enough to the water molecules "stick" together."