<span>he introduced his law of triads. each triad was a group of three elements</span>
Answer:
13.20 cm/s is the rate at which the water level is rising when the water level is 4 cm.
Explanation:
Length of the base = l
Width of the base = w
Height of the pyramid = h
Volume of the pyramid = 
We have:
Rate at which water is filled in cube = 
Square based pyramid:
l = 6 cm, w = 6 cm, h = 13 cm
Volume of the square based pyramid = V





Differentiating V with respect to dt:




Putting, h = 4 cm


13.20 cm/s is the rate at which the water level is rising when the water level is 4 cm.
Explanation:
The more reactive element replaces less reactive element during chemical reaction.
Since, potassium is more reactive than beryllium. When potassium reacts with beryllium choride, it replaces beryllium and forms potassium chloride and produces beryllium.
Answer : The correct option is (c) 
Explanation :
The given balanced chemical reaction is,

From the balanced chemical reaction, we conclude that
As, 3 moles of
react to give 2 mole of 
So, 1 mole of
react to give
moles of 
Thus, the conversion factor needed to convert the number of moles of
to the number of moles of
produced is 
Hence, the correct option is (c) 