Answer:- Density is 2.54 gram per mL.
Solution:- 
Mass of the marble ball is given as 9.513 g and it's volume is 3.75 mL.
To calculate the density of the marble ball let's plug in the values in the formula:
So, the density of the marble ball is 2.54 gram per mL.
B. People can use additional conservation tactics, like sometimes bicycling.
Explanation:
The use of bicycle to cover short distances would be good change in change in behavior that would enhance the conservational tactics in using fossil fuels.
Most hybrid cars still use gasoline. Although they have dualized energy sources.
- Driving hybrid cars more often will not curb the conservation drive for fossil fuel. It will increase more demand for it.
- Driving separate hybrid cars will not solve conservation issue of fossil fuels.
- Driving the car more is no efficient way to curb the reliance on fossil fuels.
The use of bicycles to cover maybe short distances will be a good approach to conserving more fossil fuels.
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Answer:
6.574 g NaF into 300ml (0.25M HF) => Bfr with pH ~3.5
Explanation:
For buffer solution to have a pH-value of 3.5 the hydronium ion concentration [H⁺] must be 3.16 x 10⁻⁴M ( => [H⁺] = 10^-pH = 10⁻³°⁵ =3.16 x 10⁻⁴M).
Addition of NaF to 300ml of 0.25M HF gives a buffer solution. To determine mass of NaF needed use common ion analysis for HF/NaF and calculate molarity of NaF, then moles in 300ml the x formula wt => mass needed for 3.5 pH.
HF ⇄ H⁺ + F⁻; Ka = 6.6 x 10⁻⁴
Ka = [H⁺][F⁻]/[HF] = 6.6 x 10⁻⁴ = (3.16 x 10⁻⁴)[F⁻]/0.25 => [F⁻] = (6.6 x 10⁻⁴)(0.25)/(3.16x10⁻⁴) = 5.218M in F⁻ needed ( = NaF needed).
For the 300ml buffer solution, moles of NaF needed = Molarity x Volume(L)
= (5.218M)(0.300L) = 0.157 mole NaF needed x 42 g/mole = 6.574 g NaF needed.
Check using the Henderson - Hasselbalch Equation...
pH = pKa + log ([Base]/[Acid]); pKa (HF) = 3.18
Molarity of NaF = (6.572g/42g/mole)/(0.300 L soln) = 0.572M in NaF = 0.572M in F⁻.
pH = 3.18 + log ([0.572]/[0.25]) ≅ 3.5.
One can also back calculate through the Henderson -Hasselbalch Equation to determine base concentration, moles NaF then grams NaF.
Answer: Nerve cells within the nervous system that are in charge of converting external stimuli from the organism's environment into internal electrical impulses.
