Answer:
![\boxed{\text{B and C }}](https://tex.z-dn.net/?f=%5Cboxed%7B%5Ctext%7BB%20and%20C%20%7D%7D)
Explanation:
In a single-displacement reaction, one element exchanges partners with another element in a compound.
![\textbf{A. } \rm Fe + 2HCl \longrightarrow FeCl_2 + H_2](https://tex.z-dn.net/?f=%5Ctextbf%7BA.%20%7D%20%5Crm%20Fe%20%2B%202HCl%20%5Clongrightarrow%20FeCl_2%20%2B%20H_2)
This is a single-displacement reaction, because the element Fe exchanges partners with H in HCl.
![\textbf{B. } \rm KOH + HNO_3 \longrightarrow H_2O + KNO_3](https://tex.z-dn.net/?f=%5Ctextbf%7BB.%20%7D%20%5Crm%20KOH%20%2B%20HNO_3%20%5Clongrightarrow%20H_2O%20%2B%20KNO_3)
This is not a single-displacement reaction, because it is a reaction between two compounds.
This is a double displacement reaction in which the K⁺ and H⁺ cations change partners with the anions.
![\textbf{C. } \rm Na_2S + 2HCl \longrightarrow 2NaCl + H_2S](https://tex.z-dn.net/?f=%5Ctextbf%7BC.%20%7D%20%5Crm%20Na_2S%20%2B%202HCl%20%5Clongrightarrow%202NaCl%20%2B%20H_2S)
This is not a single-displacement reaction. It is another double displacement reaction, in which the Na⁺ and H⁺ cations change partners with the anions.
![\textbf{D. } \rm Ca + 2HOH \longrightarrow Ca(OH)_2 + H_2](https://tex.z-dn.net/?f=%5Ctextbf%7BD.%20%7D%20%5Crm%20Ca%20%2B%202HOH%20%5Clongrightarrow%20Ca%28OH%29_2%20%2B%20H_2)
This is a single-displacement reaction, because the element Ca exchanges partners with H in H₂O.
are not single-displacement reactions.
The typically bald, rocky, or sandy surfaces in desert climates hold little moisture and evaporate the little rainfall they receive.
The time the chocolate bar could power the laptop in hours is 0.00233 hrs.
Since 200 Calories of chocolate bar were burned to power the 100 Watt laptop, we need to find the number of joules on energy in 200 calories of chocolate bar.
Knowing that 4.2 Joules = 1 Calorie, then
200 Calories = 200 × 1 calorie = 200 × 4.2 Joules = 840 Joules
Since the power required by the laptop is 100 W = 100 J/s and Power, P = energy/time
so, time = energy/power
So, the time for the laptop to use 840 J of energy from the chocolate bar at a rate or power of 100 W = 100 J/s is
time = 840 J ÷ 100 J/s = 8.4 s
So, the time in hours is 8.4 s ÷ 3600 s/1 h = 0.00233 hrs (since 1 hr = 3600 s)
So, the time the chocolate bar could power the laptop in hours is 0.00233 hrs.
Learn more about time to power here:
brainly.com/question/17732603
I believe the answer is A. Iron