A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room?

Identify the incorrect statement among the following :

The equivalent conductances of two strong electrolytes at infinite dilution in H₂O (where ions move freely through a solution) at 25^oC are given below:
$$ \wedge _{C{H_3}COONa}^o$$ = 91.0 S cm²/equiv
$$ \wedge _{HCl}^o$$ = 426.2 S cm²/equiv
What additional information/quantity one needs to calculate $$ \wedge ^o$$ of an aqueous solution of acetic acid?

The cell, Zn | Zn²⁺ (1M) || Cu²⁺ (1M) | Cu($$E_{cell}^o$$ = 1.10V) was allowed to be completely discharged at 298 K. The relative concentration of Zn²⁺ to Cu²⁺ $$\left[ {{{\left[ {Z{n^{2 + }}} \right]} \over {\left[ {C{u^{2 + }}} \right]}}} \right]$$ is