Oil at 150°c flows slowly through a long, thin-walled pipe of 25-mm inner diameter. the pipe is suspended in a room for which the air temperature is 20°c and the convection coefficient at the outer tube surface is 11 w/m2·k. estimate the heat loss per unit length of tube, in w/m. assume the pipe is long and the oil flow is fully developed.
also: why do we need to assume the velocity of the oil is slow?

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).

the answer is c. nacl

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2