The decay constant (λ) for a radioactive substance can be calculated using the formula:
λ = ln(2) / T
Where:

• λ is the decay constant.
• ln(2) is the natural logarithm of 2, which is approximately 0.6931.
• T is the half-life of the radioactive substance.

In your case, the half-life (T) is given as 2 seconds. Now, you can plug this value into the formula to calculate the decay constant:
λ = 0.6931 / 2
λ ≈ 0.3466 s⁻¹
So, the decay constant for this radioactive substance is approximately 0.3466 per second (s⁻¹).